U.S. patent number 3,627,076 [Application Number 05/089,546] was granted by the patent office on 1971-12-14 for extensible ladder construction.
This patent grant is currently assigned to Industrial Ladder Company. Invention is credited to Merritt A. Robinson.
United States Patent |
3,627,076 |
Robinson |
December 14, 1971 |
EXTENSIBLE LADDER CONSTRUCTION
Abstract
An extensible ladder construction of a type employing first and
second sections extensible lengthwise relative to each other
wherein the sections each comprise a pair of laterally spaced
elongated stringers and tread members uniformly spaced
longitudinally of each section and carried at their opposite ends
by the stringers is arranged whereby the stringers are of channel
shaped cross section to provide, in each instance, a web and
parallel side flanges, the stringers of the first and second
sections being turned 180.degree. relative to each other and with
the ends of tread members from both of the first and second
sections disposed between the flanges of the stringers of the first
section so as to retain the two sections in guided relation.
Accordingly, one pair of stringers includes a guide channel for
receiving a flange and the ends of the laterally extending tread
members of another pair of stringers so as to provide a double
width tread construction while increasing the thickness of the
ladder on the order of no more than 50 percent. Means for lifting
one section with respect to the other are provided which are
movable with rotation of a pulley and operable therewith for
engaging a portion of a latch means so as to move the latch between
advanced and retracted positions for engaging and releasing the two
sections. A slip drive means interposed between the pulley and the
last named means permits relative movement between the last named
means and the pulley during raising and lowering one section upon
engagement of that section with the latch means.
Inventors: |
Robinson; Merritt A. (Marin
County, CA) |
Assignee: |
Industrial Ladder Company
(Oakland, CA)
|
Family
ID: |
22218250 |
Appl.
No.: |
05/089,546 |
Filed: |
November 16, 1970 |
Current U.S.
Class: |
182/82 |
Current CPC
Class: |
E06C
1/12 (20130101) |
Current International
Class: |
E06C
1/00 (20060101); E06C 1/12 (20060101); E06c
001/12 () |
Field of
Search: |
;182/212,207,209,210,211 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Machado; Reinaldo P.
Claims
I claim:
1. In an extensible ladder, first and second ladder sections
extensible lengthwise relative to each other to form a ladder of
selectively adjustable length, each of said sections comprising a
pair of laterally spaced elongated stringers and tread members
uniformly spaced longitudinally of each section and carried at
their opposite ends by said stringers, said stringers being of
channel-shaped cross section to provide in each instance a web and
parallel side flanges, the channel-shaped cross sections of the
stringers of said first and second sections being opposed to one
another with one of the flanges and an end of the tread members of
said second section being disposed within each of the channels of
said first section, the ends of the tread members of said first
section also being disposed within each of the channels of said
first section, one side of the ends of the last named tread members
and a flange of each of the channels of said first section defining
a guideway to receive a flange and the ends of the tread members of
said second section to provide a double width tread while
increasing the ladder thickness an amount not substantially greater
than 50 percent of said first section.
2. In an extensible ladder first and second ladder sections
extensible lengthwise relative to each other, each of said sections
comprising a pair of laterally spaced elongated stringers and tread
members uniformly spaced longitudinally of each section and carried
at their opposite ends by said stringers, said stringers of said
first section being of channel shaped cross section to provide a
web and parallel side flanges, the stringers of said first and
second sections being turned 180.degree. with the ends of tread
members from both said first and second sections disposed between
the flanges of the stringers of said first section to retain said
sections in guided relation therebetween.
3. In an extensible ladder, first and second ladder sections
extensible lengthwise relative to each other, said first section
comprising a pair of elongated stringer members of channel shaped
cross section to provide a web and parallel side flanges, tread
members uniformly spaced longitudinally of said first section and
carried at their opposite ends by said stringers, the ends of said
tread members on each side of said first section being spaced from
a common one of said side flanges on said side to form a guide
channel along said stringers on each side of said first section and
defined on each side between the common one of said side flanges
and ends of said tread members, a second ladder section comprising
a pair of elongated stringer members each including a side flange,
a web portion and tread members uniformly spaced longitudinally of
said second section and carried at their opposite ends by the
last-named said web portions, the last-named said flanges and the
ends of the last-named tread members being disposed in guided
relation in said guide channels.
4. In an extensible ladder construction according to claim 3
latching means carried by one of said sections and serving to
engage the other of said sections at positions disposing the tread
members of both sections at a common level so as to provide a
double width tread for each adjacent pair of said tread
members.
5. In an extensible ladder according to claim 3 further including
lifting means for raising and lowering one of said sections
relative to the other, and latching means movable between retracted
and advanced positions and in the latter position serving to engage
and hold said one section relative to the other in an extended
position, and slip drive means interposed between the first and
last-named said means for urging said latching means toward said
advanced position while permitting said latching means to be urged
out of the path of said one section while said lifting means raises
said one section.
6. In an extensible ladder of a type having first and second ladder
sections extensible lengthwise relative to each other, and having a
rope and pulley hoist for raising and lowering one of said sections
relative to the other, said pulley being carried by said other of
said sections at the upper end thereof and said rope being trained
about said pulley, one end of said rope being secured to said one
section and the other end being free for hauling, the improvement
comprising latch means carried by said other section and movable
between advanced and retracted positions respectively into and out
of the path of said one section for engaging and holding same
relative to said other section, means movable with rotation of said
pulley and operable therewith for engaging a portion of said latch
means to move same between said advanced and retracted positions,
and slip drive means interposed between said pulley and the
last-named said means to permit relative movement between the
last-named said means and said pulley during raising and lowering
of said one section upon engagement between said one section and
said latch means.
Description
BACKGROUND OF THE INVENTION
This invention pertains to ladder constructions and more
particularly to extension ladders.
In the construction of extension ladders of a type employing a
plurality of sections wherein one section is extensible with
respect to another, it has typically been desirable to minimize the
overall thickness of the ladder construction inasmuch as two or
more ladder sections will overlap and tend to form a relatively
thick ladder construction. Therefore, the problem has been to
provide an extension ladder of minimal thickness.
In addition to the above, there has also been a continuing need for
providing an improved latch mechanism of a type which is relatively
positively acting under the hoisting action of the usual rope and
pulley hoist utilized to extend one ladder section with respect to
another.
Further, there has been the problem of constructing an extension
ladder easily handled and operated by one man using the ladder.
SUMMARY OF THE INVENTION AND OBJECTS
In general, there has been provided an extensible ladder
construction of a type employing first and second sections
extensible lengthwise relative to each other, the sections each
comprising a pair of laterally spaced elongated stringers and tread
members uniformly spaced longitudinally of each section and carried
at their opposite ends by the stringers. The stringers are of
channel shaped cross section to provide in each instance a web and
parallel side flanges, the stringers of the first and second
sections being in each instance turned 180.degree. with the ends of
tread members from both the first and second sections disposed
between the flanges of the stringers of the first section to retain
the sections in guided relation therebetween.
In short, one pair of stringers includes a guide channel for
receiving a flange and the ends of the laterally extending tread
members of another pair of stringers so as to provide a double
width tread construction while increasing the thickness of the
ladder on the order of no more than 50 percent.
In addition to the above, there is further included a lifting means
for raising and lowering one of the ladder sections relative to the
other and a latching means movable between retracted and advanced
positions. In the latter position the latching means serves to
engage and hold the raised section relative to the other in an
extended position. Slip drive means have been interposed between
the first and last named means for urging the latching means toward
its advanced position while permitting the latching means to be
pushed or struck out of the way of the raised section while the
lifting means is raising the same section.
Accordingly, means are provided which are movable with rotation of
the pulley and operable therewith for engaging a portion of the
latch means so as to move the latch means between its advanced and
retracted positions. The slip drive means interposed between the
pulley and the last-named means permits relative movement between
the last-named means and the pulley during raising and lowering of
one section (referred to as the fly section) upon engagement
between the fly section and the latch means.
In general, it is an object of the present invention to provide an
improved extension ladder construction.
It is another object of the invention to provide an extension
ladder of considerably reduced thickness in those parts thereof
where two or more sections, such as the fly and base sections,
overlap.
It is another object of the present invention to provide an
improved extension ladder characterized by a latch means positively
operated by a hoisting pulley via a slip drive mechanism for
permitting the latch means to be forced out of the path of the
moving section of ladder even during times when the latch is being
urged into the path.
The foregoing and other objects of the invention will become more
clearly apparent from the following detailed description of a
preferred embodiment .
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a side elevation section view of overlapping sections of
an extension ladder, according to the invention;
FIG. 2 is an elevation view of FIG. 1 taken along the line 2--2
thereof;
FIG. 3 is an enlarged detail view in section of aligned tread
portions of two ladder sections;
FIG. 4 is a plan view in section taken along the line 4--4 of FIG.
3;
FIGS. 5, 6, 7 and 8 show four successive stages in the positioning
of a portion of the fly section of an extension ladder relative to
latch means when raising the fly section (FIGS. 5, 6 and 7) and
lowering same (FIG. 8) to be engaged by the latch means;
FIGS. 9, 10, 11 and 12 show in side elevation four successive
stages in the positioning of a portion of the fly section of an
extension ladder relative to latch means when lowering the fly
section relative to the base section.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
As shown in FIGS. 1 and 2, an extension ladder 10 is represented by
the portions of a base and fly section respectively 11, 12 whereby
it is to be understood that fly section 12 moves up and down along
the length of base section 11.
Both sections 11, 12 are preferably molded of a suitable rigid
material such as reinforced glass fiber resin whereby the ladder
will be lightweight and nonconductive to electricity thereby
ensuring its safe usage in and about electrical wires. between the
last-named means and
Lifting means for raising and lowering fly section 12 relative to
base section 11 have been provided in the form of a hoist
consisting of a pulley 13 and hoisting rope, chain, or cable, all
referred to herein simply as a rope 14 trained about pulley 13 to
form hauling and lifting reaches 16, 17 thereof. Thus, the end of
lifting reach 17 is secured to fly section 12 at the lower end
thereof and the hauling reach 16 is free for hauling thereon so as
to hoist fly section 12 upwardly guided along base section 11 in
telescopic fashion.
Each section 11, 12 comprises a pair of laterally spaced elongated
stringers 18, 19 and tread members 21, 22 uniformly spaced
longitudinally of each section 11, 12. Tread members 21, 22 are
carried at their opposite ends by stringers 18, 19 and are
preferably formed, for strength, in the form of a U-shaped channel
configuration. The stringers 18, 19 are of channel-shaped cross
section to provide in each instance a web bounded by parallel side
flanges 23 (for stringer 18) and 24 (for stringer 19).
Stringers 18, 19 are in each instance turned 180.degree. with one
stringer flange 24' (FIG. 4) of fly section 12 and ends 21a, 22a of
tread members 21, 22 from both the first and second sections 11. 12
disposed between flanges 23 of the stringers 18 of base section 11
so as to retain the two sections 11, 12 in guided relation
therebetween.
The ends 21a, 22a of each tread member 21, 22 are retained in
molded U-shaped sockets 26, 27 forming portions of the stringers
18, 19 whereby a guide channel 28 (FIGS. 3, 4) will be defined
between the side surfaces of sockets 26 and the interior surface of
one flanges 23.
As thus arranged, sockets 27 of stringer 19 (carrying the ends of
tread members 22 therein) fit, along with flange 24', in guide
channel 28 for movement along the length of base section 11.
From the foregoing, it will be readily evident that the tread
portion has been doubled without increasing the thickness of the
ladder substantially more than 50 percent.
As now to be described, latching means have been provided to be
carried by the upper end of base section 11 so as to be movable
between retracted and advanced positions, and while in its advanced
position serves to engage and hold fly section 12 relative to base
section 11 in an extended position. Slip clutch means have also
been provided between pulley 13 and the latch means for urging the
latch means toward its advanced position to cause it to engage the
lower edge of tread members 22 while, at the same time, permitting
the latching means to be pushed or struck out of the path of fly
section 12 while pulley 13 is being used to raise fly section 12.
The latch means is also urged by pulley 13 toward its retracted
position when lowering section 12.
More particularly, as best shown in FIGS. 1 and 2, pulley 13 is
mounted upon a pulley bolt 29 and retained by a hex nut 31.
An annular dog element 32 formed with a radially projecting dog
portion 32a is mounted for rotation upon pulley bolt 29. A
resilient disc washer or compression spring 33 is carried about
pulley bolt 29 and compressed by hex nut 31 against the side
surface of dog element 32. Accordingly, dog element 32 is pinched
between the side face of pulley 13 and disc washer 33 so that upon
rotation of pulley 13, there is a tendency to rotate dog element 32
by friction engagement between the two surfaces noted above. The
friction can be enhanced by forming the confronting side face of
pulley 13 and dog element 32 with irregular surface portions.
However, upon engaging or restraining rotation of dog element 32,
it will be readily evident that pulley 13 can continue to rotate
independently thereof for purposes described below.
Latching means have been provided and carried by base section 11
for movement between advanced and retracted positions respectively
into and out of the path of fly section 12 for engaging and holding
same. The latching means is operated by dog element 32 movable with
the rotation of pulley 13 upon engagement between a dog portion 34a
of the latch means and dog portion 32a so as to move the latch
means between advanced and retracted positions.
MOre specifically, a catch member 34 formed with a detent 36 or
notch (FIG. 5) is pivotally supported to rotate with a shaft 38
carried between stringers 18 whereby catch member 34 on each end of
shaft 38 can serve to pivot about the axis thereof. A pin 35
attaches catch member 34 to shaft 38 for rotation therewith. A stop
pin 37, carried by each of members 34, rides in a notch 39 (FIG. 1)
so as to be limited in its travel and define the advanced and
retracted positions thereof. Accordingly, as shown in FIG. 1, stop
pin 37 has engaged one end of notch 39 so as to dispose detent 36
directly into the path of the lower edge of tread member 22.
The lower end of catch member 34 includes a dog portion 34a
disposed in the path of dog portion 32a.
Operation of the ladder construction as described above can best be
understood with reference to FIGS. 5 through 12 as now to be
described.
Assuming initially a downward pull on the hauling reach 16 of rope
14 there will be counterclockwise rotation of pulley 13 and, due to
the compression of the resilient annular compression spring 33,
there will tend to be counterclockwise rotation of dog element 32.
Ultimately, portion 32a of dog element 32 strikes dog portion 34a
so as to rock catch member 34 clockwise thereby disposing detent 36
into the path of the upwardly moving fly section 12 being hoisted
upwardly by reach 17. Ultimately, the upper edge of tread member 22
strikes the inclined surface 41 of catch member 34 to rotate catch
member 34 in a counterclockwise direction against the frictional
resistance of dog element 32 pinched between spring 33 and the side
face of pulley 13 (FIG. 6).
Thus, as shown best in FIG. 6, it is readily evident that the stop
pin 37 has been carried to the left side of notch 39 to permit
tread member 22 to pass upwardly. However, after tread member 22
has passed beyond catch member 34, the continued downward pulling
on reach 16 of rope 14 serves to reinsert detent 36 into the path
of fly section 12.
However, as shown best in FIG. 8, when fly section 12 is next
lowered by releasing reach 16, it will be readily evident that the
lower edge of tread member 22 will engage detent 36 as dog element
32 continues to rotate clockwise away from dog portion 34a. (As
will be seen further below, if dog element 32 rotates for a full
revolution (FIG.11), catch 34 will be retracted.)
As shown in FIG. 8, there will be present a certain amount of slack
in reach 17 so that it would be dangerous to release catches 34
without first tightening reach 17.
Accordingly, as shown in FIG. 9, downward hauling on reach 16 again
rotates dog element 32 into engagement with dog portion 34a before
releasing catch member 34. Subsequently, catch member 34 is rotated
clockwise about shaft 38 as reach 17 hoists fly section 12 upwardly
out of detents 36.
Clockwise rotation of catch member 34 is limited, of course, by
stop pin 37 as it engages the right hand edge of notch 39. Upon
being arrested by this interengagement of stop pin 37 with notch
39, pulley 13 can continue to be rotated by further downward
hauling on reach 16 by virtue of the interposition of the slip
drive formed by means of the spring washer 33 and frictional
engagement of dog element 32 between pulley 13 and washer 33.
As thus arranged, catch member 34 will be in an appropriate
position to receive the downward moving edge of tread member 22
unless it is desired to release catch member 34. Such release is
accomplished as shown in FIG. 10 by extending tread member 22 a
substantial distance beyond catch member 34 whereby upward movement
of reach 16 (FIG. 11) serves to rotate dog portion 32a
substantially a full revolution from its position as shown in FIG.
10 and into engagement with the reverse side of dog portion 34a
thereby retracting catch members 34 in a counterclockwise direction
(FIG. 11). In this manner, catch members 34 have been retracted out
of the way of the downwardly moving tread member 22 so that, as
shown in FIG. 12, tread member 22 passes clear of catch members 34
and fly section 12 can be lowered as desired.
From the foregoing, it will be readily evident that there has been
provided an improved extension ladder wherein release of the catch
members is accomplished merely by the two steps of advancing the
fly section a substantial distance up the base section on the order
of the spacing between successive tread members or rungs of the fly
section followed by downward release of the fly section whereby dog
portions 32a will engage the dog portions 34a and retract catch
members 34.
In order to relock sections 11, 12, fly section 12 is simply raised
the distance on the order of at least one-half rung of the ladder
whereby dog element 32 will have been returned to the FIG. 5
position.
Further, it will be evident that the rope-actuated locking device
allows full control of the ladder directly from the rope during all
of the functional operations of raising, lowering, locking and
unlocking the two ladder sections. In addition, the fly section 12
must travel a substantial distance of the order of one-third to
one-half the space between rungs before the locking mechanism can
act to retract catch members 34. Thus, this provides a feature
which allows the ladder to descend without the lock elements
striking each of the rungs on the one hand while permitting the
ladder to be locked by simply actuating the rope 14 on the
other.
In addition, it will be readily evident that the extension ladder
is of a considerably reduced thickness as compared to conventional
extension ladders. Accordingly, a double width tread is provided by
aligning the tread members 21, 22 in a common plane while the
overall thickness of the ladder is increased on the order of not
more than 50 percent.
* * * * *