Note: Descriptions are shown in the official language in which they were submitted.
CA 02291986 1999-12-06
'" , 1
This is a divisional of my co-pending Canadian Patent
Application No. 2,157,842 filed September 8, 1995.
The present invention relates to an extension ladder with
telescopic legs, and more particularly to an extension ladder
which can be quickly extended for use or be telescoped in a slow
and sequential manner for safe storage when it is not in use.
Moreover, the extension ladder of the present invention can be
easily assembled and is provided with automatic locking and lock
ensuring means to further ensure the safety in use.
2. Description of the Prior Art
Fig. 1 shows a conventional extension ladder with multiple
rungs. The ladder includes a pair of legs 800, 900 each
consisting of multiple tapered telescopic sections (in the
drawing, four sections of each leg are shown, separately
indicated by reference numerals 100A, 200A 300A, 400A and 100B,
200B, 300B, 400B, from bottom to top. Please see Fig. lA for
the structure of these legs), multiple rungs (in the drawing
three rungs are shown, separately indicated by reference
numerals 500, 600, 700, from bottom to top) each having a
reverse U-shaped cross section, and multiple sets of locking
mechanism for firmly locking the telescopic sections of the legs
in place after they are fully extended. The numbers of the
rungs are equal to that of the telescopic sections of the legs.
The telescopic sections are provided at their upper and middle
portions with locating holes (in the drawing,
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locating hole 111 on the upper portion of the telescopic
section IOOA, locating holes 211, 221 respectively on the
upper and the middle portions of the telescopic section
200A, and locating hole 321 on the middle section of the
telescopic section 300A are shown). The rungs 500, 600, 700
each has two ring-like ends 500A and 5008, 600A and 6008,
700A and 7048, respectively, for tightly engaging with a
pair of reduced parts 112, 212, or 312 at the upper portions
of their corresponding telescopic sections 100A, 100B; 200A,
2008; or 300A, 3008. In addition, the ring-Like ends 500A,
5008; 600A, 6008; 700A, 7008 of the rungs 500, 600, 700,
resepctively, are provided with a hole 50IA, 601A, 70IA,
respectively, corresponding to the locating holes 111, 211,
etc, on the upper portion of the telescopic sections.
Retaining rods 512, 612, etc. respectively having a push
arm 514, 614, etc. and a return spring 513, 613, etc. are
disposed near the ring-like ends 500A, 5008; 600A, 6008;
700A, 7008 of the rungs 500, 600, 700, respectively, to form
the locking mechanisms. Moreover, wear-proof plug members
222, 322, 422 with vents 222A, 322A, 422A are separately
plugged into a bottom end of the telescopic sections 100A,
200A, 300A, 400A, 1008, 2008, 300B, 4008.
Following disadvantages are found in the above-described
conventional extension ladder:
1. To assemble the extension ladder, each tapered telescopic
section thereof must be engaged into a lower section by
inserting its top end into a lower end of the lower section
one by one, and the rungs must be riveted to each top of the
telescopic sections. Such assembling procedures can not be
easily performed and the sections are not easily aligned
with one another when they are assembled according to the
above procedures.
CA 02291986 1999-12-06
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2. When the ladder is extended for use, the higher rungs are
always separated from each other and locked in place before
the lower rungs are completely pulled out to their true
positions. Therefore, the telescopic sections of the
conventional extension ladder can not be sequentially
extended and located in place one by one from bottom to top.
Also, the ladder might unexpectedly and dangerously collapse
due to operational mistake by an operator.
3. To collapse the extension-ladder, the push arms of the
locking mechanisms of the lowest rung is pulled to disengage
the retaining rod thereof from the corresponding locating
hole, allowing the next higher telescopic section to descend
until the locking mechanisms of the next higher rung touches
the lower rung below it. The contact of the higher rung
with the lower rung shall release the higher telescopic
sections from the locking mechanisms of the higher rung.
With the same movement, the remaining telescopic sections
and rungs collapse and descend one by one. However, there
is not any buffer provided between every two of the
telescopic sections, the rungs descend at a speed high
enough to unexpectedly and dangerously injure a user's
fingers. A buffer member disposed at the bottom end of each
telescopic sections might effectively slow the descending of
the rungs, the extension of the telescopic sections will,
however, become slow, too.
4. The locking mechanisms can be easily unlocked by pulling
the push arm. In the case the push arm is unexpectedly
pulled by someone, especially a child, accident might very
possibly occur.
5. The telescopic sections of the extension ladder
frictionally contact with one another when they are
CA 02291986 1999-12-06
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extended or collapsed and are therefore worn out and
become loosely connected after being used for a long period
of time.
Therefore, it is necessary to provide an improved extension
ladder to eliminate the above shortcomings.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide
an extension ladder having a safer and more effective
structure. The extension ladder of the present invention
includes two legs which each consists of a plurality of
sequentially telescoped sections. These telescopic sections
each is a straight round tube having uniform diameter which
facilitates the assembly of the telescopic sections and the
rungs.
Another object of the present invention is to provide an
extension ladder in which a plug assembly is mounted to a
bottom end of each telescopic section thereof. The plug
assembly each consists of an upper and a lower movable hook
members. When the extension ladder is in a fully extended
state, the upper hook'members may separately extend their
pointed end into retaining holes formed on the telescopic
sections. The upper hook member each has a bevelled
projection formed at an upper corner thereof on which a
lowe.= hook member of the plug assembly in the next higher
telescopic section hooks when the extension ladder is in a
fully collapsed state. When the ladder is extended and the
upper hook members separately extends into the retaining
holes on the telescopic sections, the lower hook members of
the upper plug assemblies disengage from the bevelled
CA 02291986 1999-12-06
projection of the upper hook member, allowing the telescopic
sections of the ladder to be pulled upward one by one from
bottom to top.
It is a further object of the present invention to provide
the above-mentioned extension ladder in which the plug
assembly each is provided at a bottom portion of the upper
hook member with an air cock, and at a base thereof with
an air port corresponding to the air cock, and the lowest
telescopic sections and the lowest rung are provided with
one-way valves and cooperating air tube, respectively,
whereby when the extension ladder is extended and the upper
hook members pivot to extend through the retaining holes on
the telescopic sections with their bottom portions lifted,
the air ports are opened to together with the one-way valves
and the cooperating air tube allow the air in the telescopic
sections to quickly flow through the legs and thereby
permits the ladder to be quickly extended. Or, when the
ladder is collapsed and the upper hook members pivot to
disengage from the retaining holes on the telescopic
sections with their bottom portions and accordingly the air
cocks descended, the air ports are closed to slow the air
flow in the telescopic sections and the collapse speed
thereof.
It is still a further object of the present invention to
provide an extension ladder in which locking mechanisms are
separataely mounted below the rungs centered on each end
thereof and a lock ensuring mechanism is disposed behind
each locking mechanism, whereby when the lock ensuring
mechanisms are in a locked state, the corresponding locking
mechanisms would not be unexpectedly and dangerously
unlocked by pulling an pushing arm thereof. When the top
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surface of a lower rung touches the lock ensuring mechanisms
of the next higher rung, the lock ensuring mechanisms of the
next higher rung are unlocked to free their associated
locking mechanisms, permitting the rung and the telescopic
sections of the next higher stair of the ladder to collapse.
Therefore, the rungs and the telescopic sections of other
higher stairs of the ladder can be sequentially and safely
collapsed from bottom to top in the same manner as described
above.
It is still a further object of the present invention to
provide an extension ladder in Which a wear-proof ring
member is fitted around a bottom outer periphery of each
telescopic section to prevent the same from directly
fractionally contacting with each other at their wall
surfaces lest the telescopic sections should become wearing
and loosely contacting with each other which is dangerous to
any user.
BRIEF DESCRIPTION OF THE DRAWINGS
The detailed structure and functions of the present
invention can be best understood through the following
detailed description of the preferred embodiments and
the accompanying drawings, wherein:
Fig. 1 is a fragmentary perspective view of a conventional
extension ladder, a part of which is cut away to show the
manner in which the rungs are connected to the legs of the
ladder;
Fig. lA is a fragmentary, exploded perspective view of Fig.
1 showing the structure of the leg of the ladder;
CA 02291986 1999-12-06
Fig. 2 is a fragmentary, exploded perspective view of an
extension ladder according to the present invention, a part
of which is cut away to show the assembling of a rung to two
vertically telescoped sections of the legs;
Fig. 2A is a fragmentary, sectional view taken on line A-A
of Fig. 2;
Fig. 3 is an exploded perspective view of a plug assembly
disposed at a bottom end of each telescopic section of the
present invention;
Fig. 3A is a fragmentary, assembled, sectional view showing
the positions of an upper and a lower hook members of the
plug assembly in a telescopic section of the present
invention;
Fig. 4A is a fragmentary, sectional view showing the manner
in which the telescopic sections of the legs of the present
invention is sequentially extended from a collapsed state;
Fig. 4B is a fragmentary, sectional view showing the manner
in which the telescopic sections of the legs of the present
invention is gradually collapsed from an extended state;
Fig. 5A is a fragmentary, exploded perspective view of a
locking mechanism and an associated lock ensuring mechanism
disposed in a rung other than the first or the lowest rung
of the present invention;
Fig. 5B is a fragmentray, exploded perspective view of a
general switch assembly and the associated locking mechanism
disposed in the first or the lowest rung of the present
invention;
CA 02291986 1999-12-06
Figs. 6A to 6E are fragmentary, sectional views showing the
operation of the mechanisms at different stairs of the
ladder of the present invention to collapse the same; and
Fig. 7 schematically shows another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Please refer to Fig. 2. The extension ladder of the present
invention mainly includes a pair of legs lA, 1B each
consisting of a plurality of telescopic section pairs, a
plurality of rungs each having a peripheral wall which gives
the rung a substantially reverse U-shaped cross section, a
plurality of locking mechanisms 80 for locking the
telescopic section pairs of the legs lA, 1B in place, and a
plurality of lock ensuring mechanisms 82 cooperating with
the locking mechanisms 80. The numbers of the rungs are
equal to that of the telescopic section pairs. In the first
embodiment of the present invention, reference numerals 50A
and 50 are designated to the first (the lowest) and the
other higher rungs, respectively. The telescopic sections
of the legs lA, 1B each is formed from a straight round tube
member having uniform diameter through its length. A lower
telescopic section or tube member always has an inner
diameter larger than an outer diameter of a telescopic
section or tube member immediately above it, such that every
higher telescopic section can always be fitly received in a
telescopic section immediately below it. In this
embodiment, the telescopic sections of the legs lA, 1B are
sequentially named the first tube member 10, the second tube
member 20, the third tube member 30,..... from bottom to
top.
CA 02291986 1999-12-06
_ g _
A sleeve member 60 and a plug assembly 30A are disposed on a
top end and a bottom end of each telescopic section,
respectively. Figs. 2 and 2A illustrate the manner in which
the next lower or the second rung 50 (that is, the rung
immediately above the first rung 50A) and the next lower
telescopic section pairs (that is, the second tube members
20) are assembled and locked in place. Since every other
stairs of the ladder of the present invention and either
lateral side thereof are assembled in the same manner, they
are not repeatedly explained herein. Of course, in the
actual assembling, it must begin with the lowest (that is,
the first) pair of telescopic sections and the lowest rung
from either side thereof.
I5 Please refer to Figs. 2 and 2A. To form the second stair
of
the extension ladder, first insert the third tube members
30
downward to pass through the sleeve members 60 fitted over
the top end of the second tube members 20. The third tube
members 30 each is premounted at its lower end with a plug
assembly 30A. The manner in which the plug assembly 30A
is
assembled and functions will be described in more details
later in this specification. Then, the second rung
50
is put over and engaged with a top end of the third tube
members 30. Allow the third tube members 30 and the plug
assemblies 30A at their bottom ends to e xtend into the
second tube members 20. The sleeve member 60 each is formed
at a top end with an outward extended upper flange on which
an upper and a lower locating bosses 61A, 6 1B are provided
to respectively engage with a first loca ting recess
55
formed on the second rung 50 and a second loc ating recess
21
formed near an upper edge of the second t ube member 20,
causing a first locating hole 62 to aligne with a locating
hole 54 formed at one end of the second rung 50. The second
tube members 20 are firmly engaged into two ends of
the
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second rung 50 with the sleeve members 60 between them
without the risk of turning relative to the the second rung
50. An elongated slot 51 is formed at either end of the
second rung 50 and a pair of threaded holes 52 are
oppositely formed on the peripheral wall of the second rung
50 at two sides of each slot 51, whereby fastening screws 53
can be passed through the threaded holes 52 to narrow the
slots 51 and thereby tightly bind the second rung 50 with
the second tube members 20.
The locking mechanisms 80 are disposed near the ends of the
second rung 50 on a central axis thereof and the lock
ensuring mechanisms 82 are separately disposed just behind
the locking mechanisms 80. For the first (lowest} stair of
the ladder, a general switch assembly 90 can be additionally
provided beneath the first rung 50A to cooperate with the
lock ensuring mechanism to control the extension or collapse
of the entire ladder.
Fig. 3 illustrates in details the manner in which the plug
assembly 30A and the third tube member 30 are assembled.
The plug assembly 30A each consists of a front cover 33A, a
rear cover 33B, a front insert 31A, and a rear insert 31B.
Both the front insert 31A and the rear insert 31B are formed
at their lower outer wall with a lower flange. A first pin
32I is used to pass an inner side of the front insert 31A
while threading through a first return spring 32H and
pivotally connecting an upward extended and movable upper
hook member 32A to the front insert 3IA. The upper hook
member 32A is provided on its one side surface at an upper
corner thereof with a bevelled projection 32G. A roller
32F is disposed in a hollow space formed at a front
portion of the upper hook member 32A with a somewhat
CA 02291986 1999-12-06
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flexible cover plate 32J fitted in front of the roller 32F,
such that when the upper hook member 32A extends into a
locating hole 33C formed on the front cover 33A, the
locating hole 33C is airtightly sealed. An air cock 32E is
provided at a bottom end of the upper hook member 32A. An
air port 31D is formed on a base of the front insert 31A
corresponding to the air cock 32E, whereby the air port 31D
is opened or closed when the upper hook member 32A is
pivotally turned about the first pin 32F to lift or lower
the bottom end, respectively.
A ring ear 31E is connected to an underside of the front
insert 31A. A downward extended and movable lower hook
member 32B is pivotally connected to the ring ear 31E by
means of a second pin 32D Which is threaded through a scond
reuturn spring 32C and an upper portion of the lower hook
member 32B and the ring ear 31E. The lower hook member 32B
is eccentrically positioned below the front insert 31A and
is vertically aligned With the bevelled projection 32G of
the upper hook member 32A. A projected block 31C is formed
near a front portion of the front insert 31A such that when
the front insert 3IA is placed into the third tube member 30
and fitted into a locating hole 30B thereof, the front cover
33A is engaged at its bottom flange 33H with the bottom end
of the third tube member 30 with a locating projection 33E
thereof extending into the locating hole 30B of the third
tube member 30 and vertically abutting against the projected
block 3IC of the front insert 3IA just beneath it,
permitting a front half of the plug assembly 30A to be
firmly fixed to the third tube member 30.
Then, the rear insert 31B having an air outlet 31F is
inserted into the third tube member 30, permitting an
CA 02291986 1999-12-06
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opening 33F on the rear insert 31B to communicate with an
opening 30C on the third tube member 30. Then, the rear
cover 33B is fitted around the third tube member 30 with a
bottom flange 33G of the rear cover 33B engaging into a
clearance between the bottom end of the third tube member 30
and the rear insert 31B. At this point, a locating
projection 33D on an inner wall of the rear cover 33B
extends through the opening 33F of the rear insert 31B and
engages into the opening 30C, permitting the rear half of
the plug assembly 30A to be firmly fixed to the third tube
member 30.
As shown in Fig. 4A, when the assembled ladder is to be
extended from a collapsed state, the lower hook members 32B
of the plug assemblies 30A in the next higher tube members
that are connecting with the upper hook members 32A of
the plug assemblies 30A in the lowest tube members 10 by
means of the bevelled projections 32G shall became
disengaged from the upper hook members 32A after one-way
20 valves 70 disposed near bottom ends of the first tube
members 10 are opened due to a pressure differential
resulted from the extending operation. The open of the
valves 70 permits air to be supplied to the first tube
members 10. Due to the air flowing in the tube members
forming the legs of the ladder, the telescopic sections of
the legs can be quickly extended. When the upper hook
members 32A of the plug assemblies 30A in the second tube
members 20 are moved to a point in alignment with locating
holes l0A formed on the first tube members 10, the upper
hook members 32A are sprung toward the locating holes l0A
under the spring force of the first return springs 32H
and thereby open the air ports 31D. At this point, the air
further flows upward. Meanwhile,~the lower hook members 32B
CA 02291986 1999-12-06
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of the immediately higher telescopic sections 30 are
released from the bevelled projections 32G of the upper hook
members of the second tube members 20 because they move
upward along with their upper hook members 32A. At this
point, the next higher rung, that is, the second rung 50 can
be pulled upward. After the upper hook members of the next
higher tube members 30 are moved upward and engaged into the
corresponding locating holes formed on the lower tube
members 20, the next higher rung, that is, the third rung
50, can be further pulled upward. In the same manner, other
higher telescopic sections and rungs can be sequentially
extended.
Reversely, when the ladder is downward pushed to collapse
it, the rollers 32F in front of the upper hook members 32A
in the second tube members 20 rotate when they are pressed
against an inner wall of the tube members 20, allowing the
upper hook members 32A to disengage from the locating holes
l0A of the tube members 10. A compression effect similar to
the function of a piston will be created on each of the plug
assemblies at the bottom of the tube members, forcing the
one-way valves 70 to close. Air in the tube members is
compressed and can only escape from the relatively small air
outlet 31F on the rear insert, permitting the ladder to be
collapsed slowly. When the tube members 20 are collapsed to
such an extent that the lower hook members 32B thereof
engage with the bevelled projections 32G of the upper hook
members 32A of the plug assemblies 30A in the first tube
members 10 due to the spring force of the return springs 32H
and the bevel surfaces of the bevelled projections 32G, the
higher tube members 20 are therefore connected to the Iower
tube members 10. In the same manner, the other higher tube
members are sequentially collapsed and connected to their
CA 02291986 1999-12-06
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respective immediate lower tube members, permitting the
completely collapsed ladder to be carried by just holding
its highest rung- without the risk of unexpectedly extending
again. Moreover, with the locking mechanisms, the lock
ensuring mechanisms, and the general switch assembly which
will be described in more details later, the ladder can be
automatically and sequentially collapsed stair by stair from
bottom to top.
Fig. 5A shows the locking mechanism and the lock ensuring
mechanism of the present invention, wherein the locking
mechanism 80 each consists of a sleeve member 80A, a locking
pin 81, a touch arm S1A, a push block 81B, a first pin
member 81C, and a spring 81D. The sleeve member 80A is
fitted into the locating hole 54 formed at each end of the
second rung 50. One end of the locking pin 81 is inserted
into the sleeve member 80A while the other end of the
locking pin 81 is threaded through the spring 81D to extend
into a substantially reverse U-shaped stopper 57 disposed in
the second rung 50.~ Below the locking pin 81, the first pin
member 81C is used to connect the touch arm 81A to the push
block 81B and fixedly locate them in the rung 50, such that
when the touch arm 81A is touched, the locking pin 81 can be
moved backward so as to unlock the locking mechanism 80.
The lock ensuring mechanism 82 each is composed of a locking
block 83, an unlocking touch arm 83D, a first stop screw 56,
and a third return spring 83E. The lock ensuring block 83
is formed at each side with a straight slide channel 83B to
receive a slide block 58 in the second rung 50, whereby the
lock ensuring block 83 can be vertically slided relative to
the second rung 50. The lock ensuring block 83 has an
indicating block 83C projecting from a top thereof, whereby
CA 02291986 1999-12-06
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when the lock ensuring block 83 is moved upward to a top
position of the second rung 50, the indicating block 83C
protrudes beyond a warning opening 59 formed on a top
surface of the second rung 50 to indicate the actual
operating state of the lock ensuring mechanism 82.
The lock ensuring block 83 has a pin hole 83A
provided at a .front end thereof to receive one end of
the locking pin 81 extending through the reverse U-shaped
stopper 57. The third return spring 83E and the unlocking
touch arm 83D are disposed on a side of the locking block 83
near a rear end thereof. The unlocking touch arm 83D is
formed at an outer side facing the peripheral wall of the
second rung 50 with a recess. A notch 83F is provided on a
peripheral wall surrounding the recess of the unlocking
touch arm 83D, such that when the lock ensuring block 83 is
glaced into the second rung 50 and the first stop screw 56
is screwed through the peripheral wall of the second rung
50, a lower side of the screw 56 abuts against the
peripheral wall of the recess of the unlocking touch arm 83D
to limit the lock ensuring block 83 to travel only within a
distance defined by the unlocking touch arm 83D.
Fig. 5B shows the general switch assembly 90 and the locking
mechanism 80 mounted in the first (the lowest) rung 50A of
the present invention. Since these components are somewhat
different from those mounted in other rungs 50, they are
separately described herein. The general switch assembly 90
includes a shifting wheel 90K having a shifting arm 90B, two
lock ensuring push plates 90J separately disposed at two
ends of the first rung 50A, two resilient engaging pieces
90C, and two pull rods 90A each being connected at one end
to the shifting wheel 90K and at the other end to a locking
pin 81 of the locking mechanism 80 by extending through a
CA 02291986 1999-12-06
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central pin hole 90I formed on each lock ensuring push plate
90J.
To assemble the general switch assembly 90 and the locking
mechanisms 80 to the first rung 50A, the shifting wheel 90K
is fixed to a bottom central portion of the first rung 50A
by means of extending a second pin member 90M through the
peripheral wall of the first rung 50A and through the
shifting wheel 90K. The lock ensuring push plates 90J each
is disposed in the first rung 50A With two lateral edges
thereof separately received in slide channels 90N formed on
the geripheral wall of the first rung 50A near each end
thereof, allowing the lock ensuring push plates 90J to
vertically move in the first rung 50A up and down. Second
stop screws 900 are separately screwed into the peripheral
wall of the first rung 50A to extend into dents 90P
separately formed on a side edge of the two ensuring push
plates 90J, so as to limit the lock ensuring push plates 90J
to vertically move within a distance defined by the dents
90P. The lock ensuring push plates 90J each has a
tog indicating block 83C which protrudes beyond the warning
opening 59 formed on the first rung 50A. The Iock ensuring
push plate 90J each is formed with a central pin hole 90I
and a projected block 90D. The central pin hole 90I each
has a vertical length larger than a diameter of the locking
pin 81, whereby the locking pin 81 can be moved into or out
of the central pin hole 90I. The resilient engaging pieces
90C each is engaged with the projected block 90D while its
two lower ends are received in slide channels 90Q formed in
the first rung 50A.
With the above arrangements, the extension ladder of the
present invention. can be automatically and sequentially
CA 02291986 1999-12-06
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collapsed in a manner as shown in Figs. 6A, 6B, 6C, 6D and
6E, wherein the plug assemblies 30A are only schematically
illustrated.
Fig. 6A illustrates the extension ladder in an extended and
locked state. At this point, the lock ensuring blocks 83 of
the rungs 50 and the lock ensuring push plates 90J of the
rung 50A serve to disengage the locking pins 81 from the gin
holes 83A and the central pin holes 90I, respectively,
allowing the rungs 50 and 50A to be in a firmly locked
position relative to the higher tube members and the first
tube members, respectively. Meanwhile, the resilient
engaging pieces 90C separately engage with the projected
blocks 90D of the lock ensuring push plates 90J.
Fig. 6B illustrataes the first step to collaps the extension
ladder. First, the lock ensuring push plates 90J are pushed
upward to disengage the resilient engaging pieces 90C from
the projected blocks 90D of the lock ensuring push plates
90J. At this point, the indicating blocks 83C on the top of
the lock ensuring push plates 90J moves upward to protrude
beyond the warning openings 59, indicating the rungs and the
telescopic tube members of legs are released from the safely
locked position. The indicating blocks 83C can be painted
in red color or with any other warning mark. Before using
the extension ladder, first check for any indicating blocks
83C protruded beyond the rungs. Any protruded indicating
block 83C means the ladder is not in a locked position for
safe use. At this point, the locking pins 81 each abuts
against a lower edge of the central pin holes 90I, leaving a
gap between the locking pin 81 and an upper edge of the
central pin hole 90I. The locking pins 81 at this position
are allowed to extend into the central pin holes 90I to
CA 02291986 1999-12-06
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interact with the pull rods 90A and the shifting wheel 90K.
That is, as shown in Fig. 6C, when the shifting arm 90B of
the shifting wheel 90K~is shifted to pull the pull rods 90A,
causing the locking pins 81 to move toward the center of the
rung 50A until the locking pins 81 abut against the
resilient engaging pieces 90C. At this point, the resilient
engaging pieces 90C are pushed by the locking-pins 81 to
disengage from the projected blocks 90D of the lock ensuring
push plates 90J. Meanwhile, the gaps between the locking
pins 81 and the upper edge of the central pin holes 901
cause the lock ensuring push plates 94J to move downward
which further causes the resilient engaging pieces 90C to
separate from the projected blocks 90D. Therefore, when the
locking pins 81 are further inserted into the lock ensuring
push plates 90J and be locked thereto, the lock ensuring
push plates 90J will not be stopped by the resilient
engaging pieces 90C and are therefore, permitted to slide
downward to a firmly and safely locked position. When the
shifting wheel 90K is shifted to an upper position, a
retaining leaf spring 90H on the shifting wheel 90K is
stopped by a retaining projection 90U formed on a bottom
center of the first rung SOA and the shifting wheel 90K is
prevented from further rotating and is restricted to a fully
unlocked position. This avoids undesired partial collapse
of the extension ladder due to instantaneous extension by
manual operation.
When the immediate higher rung 50 descends and the unlocking
touch arms 83D touch the first (lowest) rung 50A, as shown
in Fig. 6D, the lock ensuring blocks 83 are forced to move
upward. At the same time, the indicating blocks 83C
protrude beyond the warning openings 59. When the lock
ensuring blocks 83 move to an upmost position, the pin holes
CA 02291986 1999-12-06
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83A are aligned with the locking pins 81, allowing the
locking pins 8I to move into the pin holes 83A. Meanwhile,
the notches 83F of the unlocking touch arms 83D are aligned
with the first stop screws 56. At this point, a downward
projected gin 90F disposed on a central position of the
upper rung 50 approaches to and is aligned with a hole 90E
formed on the first {lowest) rung 50A.
As shown in Fig. 6E, before the upper rung 50 is collapsed
to its lowest position, the unlocking touch arms 83D and the
touch arms 81A connected to the locking pins 81 are forced
to pivotally turn sideward away from the lock ensuring
blocks 83 and the locking pins 81 are further moved into the
pin holes 83A, leaving the telescopic tube.members in an
unlocked state and permitting the upper rung 50 to descend.
At this point, the projected pin 90F fitly engages into the
hole 90E to press the retaining leaf spring 90H of the
shifting wheel 90K and disengage the same from the retaining
projection 90U. The shifting wheel 90K shall restore to its
home position due to the springs 81D at two ends of the
rung. At this point, the locking pins 81 are in a position
with their outer ends closing to the tube members for
readily springing into the tube members and lock the same
and the rung together.
Fig. 7 illustrates another embodiment of the present
invention, wherein a hollow fixing beam 95 is connected
between the two one-way valves 70 oppositely disposed near
the bottom of the first tubes 10 below the first rung 50.
An air tube 95A is disposed in the fixing beam 95 to
communicate with the two one-way valves 70. In addition, a
quick breather adapter 95B is provided at a center of the
fixing beam 95 to communicate the air tube 95A with the
CA 02291986 1999-12-06
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atmosphere. As mentioned previously, the upper hook member
32A may extend into the locating hole 33C on the front cover
33A and airtightly seals the locating hole 33C, whereby a
compressed air source can be connected to the quick breather
adapter 95B for the air pressure in the ladder to
automatically and quickly increase.
In conclusion, the extension ladder of the present invention
can be sequentially extended for safe use. In addition, the
extension of the ladder can be performed quickly while the
collapse thereof can be achieved in a slower manner.
Moreover, the extension ladder of the present invention can
be easily manufactured. Therefore, the shortcomings and
possible dangers in using the conventional extension ladders
as mentioned in the beginning of the specification can be
effectively eliminated.
What to be noted is the above embodiments are only used for
2D illustrating the present invention, not intended to limit
the scope thereof. Many modifications of the embodiments
can be made without departing from the spirit of the present
invention.
