Ladder extension lock

A ladder extension lock that serves as a back-up unit for an existing ladder lock system. The inventive lock releasably locks in place a section of a multiple section extension ladder. The lock is comprised of a control bar (20) planar with a rung on the fly section, having pivot pins (24) on each end. A pair of hooks (26) are attached to the pivot pins (24) and mounting blocks (28) are fastened to the side rails of the ladder and also the hooks (26). A pair of springs (37) are disposed between the bar (20) and the rung, urging the bar away from the rung. A pully (38), attached to a yoke (36), allows a halyard (46) to be engaged within a groove in the pulley (38). When an operator applies force upon the halyard (46), the bar (20) is forced upward rotating the hooks (26) to clear the rungs of the ladder while hoisting, and when pressure is quickly released, the hooks (26) rotate to their locking position and mate with the rung, creating a fail-safe mechanical lock between the rung and the side rails.

TECHNICAL FIELD 
The present invention relates to ladders with extending sections in 
general, and more specifically to an improved ladder extension lock that 
releasably retains a section of an extension ladder in an elevated 
position. 
BACKGROUND ART 
Multiple-section extension ladders conventionally use a halyard, in 
combination with a pulley and a rung engaging lock, to raise and lock the 
extended section to the required height. Previously, many types of locks 
have been used in endeavoring to provide an effective means to hold the 
section in its extended position. These locks are normally effective. 
However, there have been incidents, especially in hurried emergency 
situations, where the lock has failed causing the extended section to slip 
and cause bodily harm. 
A search of the prior art did not disclose any patents that read directly 
on the claims of the instant invention, however, the following U.S. 
patents were considered related: 
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U.S. Pat. No. 
Inventor Issue Date 
______________________________________ 
4,299,306 Hawkins 10 November 1981 
2,310,441 Klum 9 February 1943 
2,210,803 Dunn 6 August 1940 
1,964,067 Leach et al 26 June 1934 
304,420 Fox et al 6 June 1884 
750,504 Tiefel 13 May 1903 
687,945 Waggner 18 March 1901 
613,848 Seagrave 29 August 1898 
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Hawkins teaches a lock having a guideway arm attaching to two rungs 
simultaneously with a second member guiding the lock past the station of a 
ladder when the ladder is being extended or retracted. 
Klum utilizes a lock having two triangular shaped members with an opening 
therethrough rigidly attached at their apexes to a rung, the ends of which 
are rotatably received in sockets secured to the legs of the ladder. A 
rope is attached over a sheave on a tie rod on one end and to the rung on 
the other, looping through a second sheave above the rung. The operator 
uses one portion of the looped rope to disengage the hook on the lock and 
the other end for hoisting. 
Dunn practices a lock utilizing a bar formed into a loop around a rung with 
a hook on the opposite end. This bar is spring loaded and a cable is 
looped around a pulley for hoisting. In operation, tensioning the cable 
retracts the bar against the action of the spring allowing extension or 
retraction. To stop the ladder, the cable is released, suddenly extending 
the hook by spring pressure allowing the hooked end of the bar to be in 
contact with the next rung therebelow. 
Leach et al employ a hook on the end of an arm that is connected to a 
rotatable rung. The rung also has a pulley attached to a bracket. When 
pressure is exerted on a rope throug the pulley, the angle of the arm is 
such that it pulls away from the rung upon which it is resting, allowing 
the ladder to be extended. When pressure is released, the hook is rotated 
inward by gravity locking into place on the next available rung. 
Fox et al use a sheave disposed centrally on a rail over which a cord 
passes connected to an arm of a rock-shaft journaled on a rotatable shaft. 
A pair of upwardly projecting hooks are secured near the ends of the shaft 
and rotate as the rope is pulled disengaging the hooks when tension is 
applied. Release for retraction is accomplished in the reverse procedure. 
For background purposes and as indicative of the art to which the invention 
relates reference may be made to the remaining cited patents. 
DISCLOSURE OF THE INVENTION 
Extension ladders per se have been in use for many years with prior art 
pertaining to improvements recorded for over a century. A common use for 
an extension ladder is for fire fighting, where human life is involved 
during an emergency situation and safety is of prime importance. Many 
ladders specifically designed for fire service have locks that maintain 
their extended position, however, field usage has proven that the actual 
function lacks reliability as numerous accidents have been caused directly 
related to the existing prior art. It is, therefore, the primary object of 
the invention to provide a highly reliable, safe, easy to operate lock for 
fire ladders, in particular, easily adaptable to existing apparatus in kit 
form, or as originally manufactured. The invention utilizes a pair of 
pivotal rung engaging hooks that move out of the way of the next rung when 
extended and spring loaded, in a positive manner, into a locked position 
when tension on a halyard is released. This feature allows the hook to be 
deadlocked in the engaged position, except when the ladder is being 
controlled by the halyard. 
An important object of the invention provides failsafe operation of the 
lock. The normal operating procedure in extending a ladder is for one 
operator to stand at the base and hold the ladder while another person 
hoists the top section by the use of halyard, or rope, that is connected 
loopingly through a series of pulleys. If the lock malfunctions, the 
halyard breaks, or slips, in the operators hands, the upper section 
retracts at high velocity, as considerable weight is involved. This 
creates a dangerous situation for the operator, or if a hand or foot is 
positioned over a rung, the shear action of the falling section can cause 
dismemberment or serious injury. Recorded incidents and requests for 
correction are on file, such as petition file no. 187, State of 
California, Department of Industrial Relations Occupational Safety and 
Health Standards Board, dated 1 April 1985. 
Another object of the invention locates the apparatus for mechanical 
operation below the rung, or station, out of the way of the user so as not 
to create any interference. This location is convenient in that the pulley 
is in the center leaving both sides open and clear, as the center is not 
utilized during the climbing process by the user of the ladder. 
A further object of the invention allows existing ladders to be easily 
modified using a simple kit having the necessary components for the 
retrofit. This kit fits many different styles and manufacturers of two or 
three section fire ladders with only minor modification necessary to the 
ladder itself, thus increasing the utility. While existing ladders may be 
modified, original equipment for both fire ladders, and general purpose 
sectionalized ladders may equally well be accommodated using this 
invention. 
These and other objects and advantages of the present invention will become 
apparent from the subsequent detailed description of the preferred 
embodiment and the claims taken in conjunction with the accompanying 
drawings.

BEST MODE FOR CARRYING OUT THE INVENTION 
The best mode for carrying out the invention is presented in terms of a 
preferred embodiment as shown in FIGS. 1 through 9. The ladder extension 
lock is comprised of a channel shaped control bar 20 that is movably 
positioned under a rung of a multiple-section extension ladder 22 as best 
shown in FIG. 1. This bar 20 is mitered or stepped at each end and is 
installed with the legs projecting upward toward the rung of the ladder 
22. A pair of removable pivot pins 24 are attached on each end of the 
control bar 20 on the web, or on one of the upstanding legs, and extend 
outwardly. This pin 24 is flat on one end, where it attaches to the bar 
20, and round on the other, becoming the pivot point for ultimate 
connection to the ladder 22. The pin 24 is normally attached to the bar 20 
by a set of metal screws. 
A pair of rung engaging hooks 26 are rotatably connected to the pivot pins 
24 through holes located within the hook. The hook 26 has a thickness 
sufficient to maintain structural integrity of the ladder section while 
resting thereupon, and also to withstand stress loads when released. The 
hole, therefore, has sufficient strength to function independently, or a 
bushing, such as an oil impregnated sintered bronze sleeve, may be added 
for further wear resistance. The hook 26 is fabricated of a flat metallic 
plate, preferably aluminum, steel, or magnesium, and is shaped with an 
angular top with a concave surface on one side, tapering to full width and 
a notch on the other side. This hook 26 is so shaped as to grip one rung 
of the ladder 22 on one side and clear another on the opposite side as 
best shown in FIG. 2. In operation this hook 26 axially rotates outwardly 
when the control bar is urged upward toward the ladder rung clearing the 
rung above, as best shown in FIG. 3. The angular top assists this movement 
when the ladder is extended manually without using the halyard. In this 
case, the hook 26 will ride over the rungs as the ladder is extended. A 
hook stop 27 is rigidly mounted on the side of each hook 26, creating an 
obstruction, preventing the hook from over-travelling in its pivotal arc 
during the operation of hoisting or lowering. This stop 27 consists of a 
hollow spacer in conjunction with a capscrew positioned within a threaded 
hole in the hook 26, or may be any mechanical structure, such as a roll 
pin, socket head capscrew, rivet, or the like. 
A pair of mounting blocks 28, as best shown in FIGS. 1 and 4, are attached 
into the side rails of the ladder 22 immediately below a rung. These 
blocks 28 become a structural member to receive the hook 26 with swivel 
means in the form of a pivot capscrew with a bearing sleeve 30. The block 
28 is internally threaded allowing attachment from the outside a similarly 
threaded hole is located on the inside receiving the capscrew and sleeve 
30 for attachment of the hook 26. This screw and sleeve 30 provide the 
pivot point in conjunction with the control bar pivot pin 24, converting 
linear movement of the bar 20 to axial rotation of the hook 26 when the 
bar 20 is urged upward toward the rung of the ladder 22. 
A plurality of adjustable control bar stops 32, preferably two, are 
attached to the inside of the web of the control bar 20. Each control bar 
stop 32 is comprised as best shown in FIG. 4, of a threaded fastener 34, 
such as a flathead bolt, containing a spring guide sleeve 35 and a 
compression spring 37. The bolt, in turn, is locked in place on the 
control bar 20 by means of a locknut 39. The spring 37 is compressibly 
fixed between the bar 20 and the rung of the ladder 22 directly above. 
This provides continual tension on the bar 20, driving it to the maximum 
spaced relationship while maintaining the hook 26 in its retracted 
position, due to its attachment through the pins 24. 
This arrangement allows adjustment to be made between the rung and the bar 
20 by rotating the stop 34 until the proper height is achieved. Once this 
height is reached, the stop 34 is locked in placed on the control bar as 
previsouly described. 
A channel shaped pulley yoke 36, as best shown in FIGS. 4 and 8, is 
positioned under the web of the bar 20, in the middle, with the legs 
distended upward defining an attachment member. The legs of the yoke 36 
are of sufficient length to extend beyond both the bar 20 and the rungs of 
the ladder 22. The yoke 36 is attached to the bar with fastening means, 
well known in the art, and a pulley 38, having an axle 40, is rotatably 
positioned between the legs of the yoke 36. This pulley 38 has a grooved 
rim and a set of centrally located bearings for rotation. The pulley axle 
40 is comprised of a headed capscrew having a hexagonal or round head with 
solid shank, and a hexagonal headed lock nut threadably attached to the 
screw. A dowel pin with retaining rungs may also be used for the pulley 
axle 40, as an alternate embodiment. A channel shaped halyard guide 42 is 
disposed contiguously within the pulley yoke 36, separating the pulley 38 
from the ladder rung. This structure allows a halyard to run freely within 
the groove of the pulley 38 wihout binding or interference. This 
arrangement is best illustrated in FIGS. 6, 7 and 8. 
A halyard 46, in the form of a rope, such as pure manilla, of sufficient 
size to raise the ladder sections, is threaded through the pulley 38 and 
alternately through the existing hoisting pulleys 44 with one end attached 
to the ladder section and the other end loose. This pulley arrangement 
allows an operator to hoist sections of a ladder 22 from the ground as 
shown in FIG. 5. The instant invention further includes the safety 
improvements such that when the section is hoisted by the halyard 46, in 
conjunction with the pulleys 38 and 44, the control bar 20 is urged upward 
toward a rung on the butt section against spring pressure, therefore, 
pivoting the hooks 26 outwardly away from the rungs on the fly section. 
This rotary movement allows the hooks 26 to pass by any number of rungs 
without interference while being hoisted or retracted. However, when 
tension is quickly released, even for a short distance, the hooks 26 will 
rotate to their locking position by the pressure of the springs 32. Thus, 
in the event of an accidental loosening grip on the halyard, breakage, or 
other unexpected release, the invention allows the ladder 22 to secure 
itself in the extended position, creating a fail-safe condition. 
There are many arrangement of halyards and pulleys, depending upon the 
number of sections to be raised, the weight and orientation of the fly and 
butt sections, therefore, this prior art has little consequence to the 
invention, except that some arrangement is necessary to allow the halyard 
to be pulled from a position above the apparatus thus disclosed. 
It will, therefore, be seen that the ladder extension lock serves as a 
fail-safe back-up unit to an existing ladder lock system affixed to a 
multiple section ladder. 
While the invention has been described in complete detail and pictorially 
shown in the accompanying drawings, it is not to be limited to such 
details, since many changes and modifications may be in the invention 
without departing from the spirit and the scope thereof. Hence, it is 
described to cover any and all modifications and forms which may come 
within the language and scope of the claims.