JPH07247776A - Extensible ladder provided with mechanism for preventing working rope from slackening - Google Patents

Abstract

PURPOSE:To prevent a walker's foot from being caught by part of a working rope left over, and to insure the safety of a worker on an extensible ladder, by a method wherein the extensible ladder saves a worker the trouble of putting the part of the working rope and a lock-releasing rope left over round the extensible ladder and prevents the worker from forgetting the trouble above- mentioned, during the extension or retraction thereof. CONSTITUTION:At the upper part of a lower ladder 22, a first roller 28 and an upper fixation part 30 are respectively provided above and bellow and at the lower part thereof, a second roller 29 and a lower fixation part 31 are respectively provided above and below. On the other hand, at the lower part of an upper ladder 23, a third roller 35 and a fourth roller 36 are respectively provided above and below. One end of a working rope 24 is fixed to the upper fixation part 30, and the other is fixed to the lower fixation part 31 after the rope is reeved through the third roller 35, the first roller 28, the second roller 29 and the fourth roller 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telescopic ladder that is used by being stretched when working in high places, and particularly when the telescopic ladder is stretched, the actuating rope does not sag. Regarding

[0002]

2. Description of the Related Art As a conventional telescopic ladder, the one shown in FIGS. 13 to 18 is known.
Shows a state where the telescopic ladder is contracted, and FIGS. 16 to 18 are diagrams showing a state where the telescopic ladder is extended.

In these figures, a telescopic ladder 1 is mainly composed of a lower ladder 2 and an upper ladder 3, and an operating rope 4 for slidingly expanding and contracting the lower ladder 2 and the upper ladder 3. The lower ladder 2 includes a column 5 and a plurality of ladder bars 6 orthogonal to the column 5,
It is composed of a lower ladder roller 7 provided on the upper end of the column 5, and a fixing portion 8 for fixing one end of the working rope 4.
The upper ladder 3 is composed of two parallel pillars 9, a plurality of ladder bars 10 orthogonal to the pillars 9, and an upper ladder roller 11 provided at the lower end of the pillar 9.

As shown in FIG. 15, the operating rope 4 has one end fixed to the fixing portion 8 and then the upper ladder roller 11
After being turned to the upper side through the lower side, passed through the upper side of the lower ladder roller 7 and turned to the lower side, and arranged along the column portion 5 of the lower ladder 2. Then, by pulling the operating rope 4 downward along the support column 5 of the lower ladder 2,
As shown in FIGS. 6 to 18, the actuation rope 4 has a fixed portion 8
The upper ladder roller 11 is lifted up with the support point as a supporting point, and as a result, the upper ladder roller 11 approaches the lower ladder roller 7 side, thereby raising the upper ladder 3 with respect to the lower ladder 2.

Then, in a state where the upper ladder 3 is extended with respect to the lower ladder 2, as shown in FIG. 17, the lowermost rail 10 of the upper ladder 3 and the uppermost rail 6 of the lower ladder 2 are connected. 1
The two are fixed to each other by the two, which prevents the telescopic ladder from shrinking and the worker being dropped and injured during the work.

In order to prevent the telescopic ladder 1 from falling over, the telescopic ladder 1 is locked to an upper suspension line.
A locking means (not shown) is provided. The locking means is a hook provided on the upper part of the upper ladder 3, a lock mechanism for preventing the hook from coming off the suspension line, and the lock mechanism for the ground or It is provided with a lock release rope for releasing from the floor surface.

[0007]

However, in the above-mentioned conventional telescopic ladder, when the operation rope 4 is pulled to raise the upper ladder 3, the upper ladder roller 11 causes the lower ladder 2 to move as shown in FIG. The operating rope 4 has an extra length as much as it comes closer to the fixed portion 8, and the extra length of the operating rope 4 is scattered on the lower part of the lower ladder 2. Therefore, a person who walks under the ladder while performing work at a high place using the telescopic ladder 1 may fall on the ladder by catching his / her foot on the extra length of the operating rope 4. There is a problem that it is very dangerous for a worker at a high place on the telescopic ladder 1 to perform work while leaving the long rope 4 left unattended.

Therefore, when the telescopic ladder 1 is used while being stretched, the slack of the operating rope 4 is treated by winding the extra length portion of the operating rope 4 around the column 5 of the lower ladder 2 and the like. However, it is very complicated work to perform the winding work every time the work is performed, and there is a problem that the work efficiency is reduced.

Further, when the telescopic ladder 1 is contracted, the lock release rope has an extra length in the lock release rope by the amount of contraction of the upper ladder 3 and becomes an obstacle during transportation.
When the telescopic ladder is carried around by winding it around the ladder bar 6, and when the telescopic ladder is used, it must be unwound and the work is complicated, and careless operation is required even when the telescopic ladder is extended. In order to prevent this, it is necessary to wind the end of the lock release rope around the ladder rail, etc., which is troublesome.

The present invention has been made to solve the above-mentioned problems, and when expanding and contracting a telescopic ladder, it is possible to eliminate the trouble of winding the extra length of the operating rope and the lock release rope around the telescopic ladder and to wind the telescopic ladder. By preventing forgetting, an extensible ladder with an slack prevention mechanism for the operating rope that can ensure the safety of the operator on the extension ladder without the pedestrians catching their feet on the extra length of the operating rope. It is intended to be provided.

[0011]

In order to solve the above problems, the present invention is a telescopic ladder in which an upper ladder and a lower ladder are slidably expanded and contracted by an operating rope, and the operating rope is Both ends are fixed to the lower ladder and are engaged again with the rollers provided on the lower ladder via the rollers provided on the upper ladder. By moving the operation rope, the upper ladder is moved. The roller of (1) moves integrally with the upper ladder in a state where the operating rope is always tensioned.

According to the second aspect of the present invention, the first roller and the upper fixing portion are provided on the upper and lower portions of the lower ladder,
A second roller and a lower fixing portion are provided at a lower portion of the upper ladder, a third roller and a fourth roller are provided at a lower portion of the upper ladder, and one end of the operation rope is fixed to the upper portion. The other end of the actuation rope is fixed to the lower fixing portion through the third roller, the first roller, and the second roller through the fourth roller. It has a feature.

According to a third aspect of the present invention, there is provided an expansion and contraction ladder in which the upper ladder and the lower ladder are slidably expanded and contracted, and a locking means for locking the suspension wire is provided on the upper part of the ladder. The means comprises a hook portion provided on the upper portion of the upper ladder, and a lock mechanism for preventing the hook portion from coming off the suspension line,
One end of an operating rope for releasing the locked state is attached to an end portion of the lock mechanism, and the other end portion of the operating rope is a lower roller provided at a lower portion of the lower ladder and an upper roller provided at an upper portion thereof. It is characterized in that it is fixed via an elastic body to a fixing portion provided at the lower part of the upper ladder via.

According to a fourth aspect of the present invention, the first roller and the second roller are provided on the inner side surface of the support portion of the lower ladder, and the third roller and the fourth roller are the upper ladder. It is characterized in that the upper roller and the lower roller are provided on the inner side surface of the column portion, and the upper roller and the lower roller are provided on the outer surface of the column portion of the lower ladder.

[0015]

According to the first aspect of the present invention, since both ends of the operating rope are fixed to the lower ladder, the operating rope is provided on the upper ladder by pulling the operating rope so that the fixing portions at both ends serve as support points. The roller is pulled in a predetermined direction, and along with this, the upper ladder moves together with the roller.

According to a second aspect of the present invention, a first operation rope is provided.
When the space between the first roller and the second roller is pulled toward the lower fixed portion side, the third roller is pulled toward the upper fixed portion side by the operation rope, and the third roller approaches the first roller and the fourth roller. Roller away from the second roller so that the upper ladder slides against the lower ladder.
Further, when the space between the first roller and the second roller of the actuation rope is pulled toward the upper fixed part, the fourth roller is pulled toward the lower fixed part by the actuation rope, and the fourth roller moves toward the second fixed part. The third roller moves away from the first roller as it approaches the roller side, and as a result, contracts while sliding the upper end against the lower ladder.

According to a third aspect of the present invention, when the upper ladder is extended with respect to the lower ladder, the fixing portion of the upper ladder approaches the upper roller of the lower ladder and at the same time, the fixing portion of the upper ladder moves away from the lower roller. , This does not cause the actuation rope to sag. In addition, when the space between the lock mechanism of the operating rope and the lower roller is pulled to the lower roller side, the lock mechanism is released and the amount of the pulled operating rope is absorbed by the elastic body on the fixed side. There is no slack.

According to the fourth aspect of the invention, the first roller, the second roller, the third roller, and the fourth roller are provided on the inner side surfaces of the columns of the upper ladder and the lower ladder. A person passing by on the outer side does not accidentally touch the actuation rope during work. Further, since the upper roller and the lower roller are provided on the outer side surface of the column portion of the lower ladder, the mechanism for expanding and contracting the ladder and the lock releasing mechanism can be mounted on the same expandable ladder.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. 1 to 6 show an embodiment of the present invention, in which reference numeral 21 denotes an expansion / contraction ladder with an operation rope slack preventing mechanism (hereinafter simply referred to as "expansion / contraction ladder"). In these figures, a telescopic ladder 21 includes a lower ladder 22 and an upper ladder 23, an operating rope 24 for slidingly expanding and contracting the lower ladder 22 and the upper ladder 23, and rollers for attaching the operating rope 24 to the upper and lower ladders. Mainly composed of a fixed part.

The lower ladder 22 is composed of two pillars 26 and a plurality of ladder rails 27 fixed orthogonally between the pillars 26 to form a ladder body, and the inner surface of each of the two pillars 26. Is provided with a first roller 28 near the upper end and a second roller 29 near the lower end. Further, the upper fixing portion 3 is provided near the lower portion of the first roller 28.
0 is fixed, and a lower fixing portion 31 is fixed near the lower portion of the second roller 29.

Further, the upper ladder 23 is composed of two pillars 33.
And a plurality of ladder rails 3 fixed orthogonally between them.
A ladder main body is constituted by 4 and 4, and on each inner side surface of each of the two columns 33, a third roller 35 is provided on the upper side near the lower end portion, and a fourth roller 36 is provided on the lower side. . The pillar portions 26 and 33 of the lower ladder 22 and the upper ladder 23 are formed to have the same width and the same length as the pillar portion 26 of the lower ladder 22, and these pillar portions 26 and 33 are not shown. They are connected by a sliding mechanism so as to be slidable and parallel to each other in the longitudinal direction.

The lower ladder 22 and the upper ladder 23 are made extendable and contractible by an actuation rope 24, and one end of the actuation rope 24 is fixed to the upper fixing portion 30 while the other is, as shown in FIG. The end is guided downward and the third roller 3
5 is turned upside down via the lower side of the first roller, then is turned upside down via the upper side of the first roller, and further passed under the second roller 29 and the fourth roller 36.
The direction is inverted downward via the upper side of the, and finally fixed to the lower fixing portion 31. As the operating rope 24, a rope which is less stretchable and strong may be used. The rollers 28, 29, 35 and 36 have little friction with the operating rope 24 and rotate on the columns 26 and 33. It is freely and firmly fixed.

Further, a connecting member 37 is attached to the lowermost ladder rail 34 of the upper ladder 23, and the ladder rail 34 is inserted into the base end of the connecting member 37 so that the ladder rail 34 is secured. An engaging portion 27a that is rotatable about an axis and that is engaged with the ladder rail 27 of the lower ladder 22 is formed at the tip of the connecting member 37. The ladder rail 34 of the upper ladder 23 and the lower ladder 2 are formed.
With the second ladder rail 27 adjacent to the same height, the connecting member 27 is rotated around the ladder rail 34 to lock the locking portion 37a to the ladder rail 27, whereby the upper ladder 23 at the time of use.
Is configured so as not to drop to the lower ladder 22 side.

In the telescopic ladder 21 of the present embodiment constructed as described above, when the upper ladder 23 is extended and used, as shown in FIGS. 4 to 6, the lower ladder 22 is placed on the ground or floor. In a state in which the operating rope 24 is held upright, the space between the first roller 28 and the second roller 29 of the operating rope 24 is fixed to the lower fixing portion side 3
When pulled to 1, the third roller 35 is pulled toward the upper fixed portion 30 side by the operation rope 24 with the upper fixed portion 30 as a support point. Therefore, the third roller 35 approaches the first roller 28, while the fourth roller 36 moves away from the second roller 29.

As a result, the upper ladder 23 ascends while sliding with respect to the lower ladder 26 without the operation rope 24 sagging. Then, when the upper ladder 23 has risen to the vicinity of the uppermost portion of the lower ladder 22, the connecting member 37 causes the upper ladder 2 to rise.
The third ladder rail 34 is fixed to the ladder rail 27 of the lower ladder 22 to prevent it from falling.

When the upper ladder 23 is contracted and moved to another place, the actuating rope 24 is once pulled to the lower fixing portion 31 side so that the engaging portion 37a of the connecting member 37 is the ladder of the lower ladder 22. When removed from the crosspiece 27, the upper ladder 23 later falls to the lower ladder 22 side by its own weight. At that time, the fourth roller 36 approaches the second roller 29 and the third roller 35 moves to the first roller 35. Go away from the roller 28, the upper ladder 23
Contracts while sliding on the lower ladder 22, but the actuation rope 24 does not sag.

Next, a second embodiment of the present invention will be described with reference to FIGS. The second embodiment is the same as the first embodiment.
A locking means is provided on the upper part of the expansion / contraction ladder of the embodiment, and the upper part of the expansion / contraction ladder is hooked to a suspension line or the like by this locking means for use. In these figures, the same or similar parts as those shown in the above embodiment are designated by the same reference numerals, and the description thereof will be omitted. In addition, regarding the expansion / contraction mechanism by the operation rope 24 shown in the above-mentioned first embodiment, the support columns 26, 3 of the upper and lower ladders are used.
Illustration is omitted as it is equipped inside 3.

The locking means 41 is provided on the upper ladder 23 and comprises a hook portion 42 for hooking the telescopic ladder 21 on the suspension wire 39, and a lock mechanism 43 for preventing the suspension wire from coming off from the hook portion 42. The lock mechanism 43 includes a lock release rope 44 as an operation rope for releasing the locked state, and a lock release rope 44.
An upper roller 45 and a lower roller 46 attached to the outer surface of the column portion 26 of the lower ladder 22 and a fixing portion 48 for fixing the end portion of the unlocking rope 44 via a spring (elastic body) 47 are provided. There is.

The hook portion 42 is formed by fixing a U-shaped metal fitting to the upper portion of the upper ladder 23, and the lock mechanism 43 has a shaft 49 near the base end portion of the rod-shaped member to attach it to the hook portion 42. It is rotatably rotatably supported, and its tip end is locked to the inside of the hook portion 42 by its own weight. One end of the unlocking rope 44 is attached to the rope fixing portion 43a on the base end side. It is installed. Further, the other end of the unlocking rope 44 turns upward via the lower side of the lower roller 46 provided at the lower end of the outer surface of the pillar portion 26 of the lower ladder 22, and then turns to the upper side of the pillar portion 26. It is turned to the lower side via the upper side of the upper roller 45 provided on the outer side surface, and is further fixed to the fixing section 48 provided on the lower portion of the outer side surface of the support section 33 of the upper ladder 23.

The lock releasing rope 44 may be a thin rope which is thin and has little elasticity and is hard. Further, the upper and lower rollers 45 and 46 have little friction with the rope, and may be rotatably and firmly attached to the column 26 of the lower ladder 22.

The telescopic ladder of the second embodiment constructed as described above has the same effects as the first embodiment, and
The locking means 41 of this embodiment includes an upper ladder 23 and a lower ladder 22.
In the state where and overlap and contract, the lock release rope 44
Are arranged so as to intersect between the upper and lower fixed ends 43a and 48 and the upper and lower rollers 45 and 46, but when the upper ladder 23 is raised and extended from the lower ladder 22, the rope fixing portion 43a is lowered. Since the fixing portion 48 approaches the upper roller 45 by the distance from the upper roller 45 of the ladder 22, the unlocking rope 44 does not sag.

Then, when the hook 42 is locked to the suspension wire 39 while the telescopic ladder 21 is extended, the lock mechanism 43 is automatically pushed up and released, and in this state, the hook 42 is locked to the suspension wire 39. Then, the lock mechanism 43 is automatically rotated by its own weight and locked on the hook 42 side to be in the locked state.

Further, the fixed end 43 of the unlocking rope 44
When the space between “a” and the lower roller 46 is pulled toward the lower roller 46, the lock mechanism 43 pivots around the shaft body 49, the tip end is separated from the hook 42, and the locked state is released and the lock is released. The amount of pulling the rope 44 is the elastic body 47.
Is absorbed by the contraction of the
There is no slack. In this state, when the hook 42 is detached from the suspension line 39 and the upper ladder 23 is dropped to the lower ladder 22 side to contract the telescopic ladder 21, a reverse action to the above-described extension occurs, and the lock release rope 44 has an extra length. Does not occur.

The present invention has been described in detail above with reference to the drawings, but it goes without saying that the present invention is not limited to the above embodiments.

For example, in the above-mentioned embodiment, the pair of first, second, third and fourth rollers are provided on the inner side surfaces of both supporting columns of the upper and lower ladders, respectively, but the present invention is not limited to this. A pair may be provided on the outer side surface of the section, or one may be provided on one of the left and right column sections. Furthermore, the positional relationship between each roller and the upper and lower fixing portions may be any positional relationship in which the movement of the actuation rope is not restricted and each roller is rotatable.

Further, it is needless to say that the above-mentioned locking means can be provided separately in the conventional expansion and contraction ladder, and may be provided on the inner side surface of the supporting column. Further, in the above-described embodiment, the spring is used as the elastic body, but any elastic material such as a rubber cord that can be expanded and contracted and is not easily broken may be used. The shape of the hook is not particularly limited as long as it can be locked to the suspension wire.

[0037]

As described above, according to the present invention, since both ends of the operating rope are fixed to the lower ladder, by pulling the operating rope, the rollers provided on the upper ladder can be moved to a predetermined position by the operating rope. As the upper ladder moves in relation to the lower ladder, the actuating rope is displaced as the roller moves, and the actuating rope is always maintained in a tensioned state. There is no extra length. Therefore, work safety can be ensured and work efficiency can be improved.

According to a second aspect of the present invention, a first operation rope is provided.
When the space between the first roller and the second roller is pulled toward the lower fixed portion side, the third roller is pulled toward the upper fixed portion side by the operation rope, and the third roller approaches the first roller and the fourth roller. Since the roller of is separated from the second roller, the length of the operating rope always moves with a constant tension,
No extra length is generated, and when the space between the first roller and the second roller of the operating rope is pulled toward the upper fixed portion side, the fourth roller is pulled toward the lower fixed portion side by the operating rope. , The fourth roller approaches the second roller side, and the third roller moves away from the first roller, so that the length of the actuation rope always moves with a constant tension,
No extra length is generated. Thus, even if the upper ladder and the lower ladder are expanded and contracted, no extra length is generated in the operating rope, and during the work at height using the expandable ladder of the present invention,
The extra-long rope will not be accidentally pulled and the telescopic ladder will not fall over, making it possible to ensure work safety and
The work of winding the extra length rope around the column of the lower ladder can be omitted, and the work efficiency can be improved.

According to the third aspect of the present invention, when the upper ladder is extended with respect to the lower ladder, the fixing portion of the upper ladder approaches the upper roller of the lower ladder and at the same time, the fixing portion of the upper ladder moves away from the lower roller. As a result, it is possible to prevent an extra length from being generated in the operating rope. Further, when the space between the lock mechanism side and the lower roller of the lower operation rope is pulled to the lower roller side, the lock mechanism is released and the pulled operation rope is absorbed by the elastic body on the fixed portion side. It is possible to prevent an extra length from being generated in the operating rope. Therefore, the extra length of the work rope is not accidentally caught on the legs even during work, and the safety of the work can be ensured, and the labor of unwinding and unwinding the extra length of the work rope is saved. Therefore, the work efficiency can be improved.

According to a fourth aspect of the present invention, the first roller, the second roller, the third roller, and the fourth roller are provided inside the column portions of the upper ladder and the lower ladder, and therefore, the work is performed. It is possible to prevent a person passing in the vicinity from accidentally touching the actuation rope and tipping over the ladder, and it is possible to safely perform work on the telescopic ladder. Further, since the upper roller and the lower roller are provided outside the column portion of the lower ladder, the mechanism for extending and retracting the ladder and the locking means can be mounted on the same extendable ladder, and the unlocking operation can be performed easily. easy.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of an expansion / contraction ladder with an operation rope slack prevention mechanism of the present invention, in a state in which the expansion / contraction ladder is contracted.

FIG. 2 is a sectional side view taken along the line AA of the above embodiment.

FIG. 3 is an explanatory diagram illustrating a drive mechanism of the operation rope of the above-described embodiment.

FIG. 4 is a front view of the stretchable ladder of the above embodiment in a stretched state.

FIG. 5 is a side view taken along the line BB of the above embodiment.

FIG. 6 is an explanatory diagram illustrating a drive mechanism of the actuation rope of the above embodiment.

FIG. 7 is a front view showing a second embodiment of the expansion / contraction ladder with the operation rope slack prevention mechanism of the present invention, in a state in which the expansion / contraction ladder provided with the locking means is contracted.

FIG. 8 is a cross-sectional side view taken along line CC of the second embodiment.

FIG. 9 is an explanatory diagram illustrating a drive mechanism of an operating rope according to a second embodiment.

FIG. 10 is a front view of the telescopic ladder of the second embodiment in a stretched state.

FIG. 11 is a side view of the DD cross section of the second embodiment.

FIG. 12 is an explanatory diagram illustrating a drive mechanism of an operation rope (lock release rope) of the locking means of the second embodiment.

FIG. 13 is a front view of a conventional retractable ladder in a contracted state.

FIG. 14 is a side view of the conventional expandable ladder taken along line EE.

FIG. 15 is an explanatory diagram illustrating a drive mechanism of a locking unit of a conventional telescopic ladder.

FIG. 16 is a front view of a conventional telescopic ladder in a stretched state.

FIG. 17 is a side view taken along the line FF of FIG.

FIG. 18 is an explanatory diagram illustrating a drive mechanism of a locking unit in a state where the expansion ladder of FIG. 16 is extended.

[Explanation of symbols]

21 Telescopic Ladder (Expandable Ladder with Actuating Rope Slack Prevention Mechanism) 22 Lower Ladder 23 Upper Ladder 24 Operating Rope 26, 33 Support Part 28 First Roller 29 Second Roller 30 Upper Fixing Part 31 Lower Fixing Part 35 Third Roller 36 Fourth Roller 41 Locking Means 43 Locking Mechanism 45 Upper Roller 46 Lower Roller 47 Spring (Elastic Body) 48 Fixed Part

Claims (4)

[Claims] 1. An expansion ladder in which an upper ladder and a lower ladder are slidably expanded and contracted by an operation rope, the operation rope having both ends fixed to the lower ladder,
It is engaged again with the roller provided on the lower ladder via the roller provided on the upper ladder, and by moving the operating rope, the roller of the upper ladder constantly tensions the operating rope. In the state, the telescopic ladder with the operation rope slack prevention mechanism moves integrally with the upper ladder. 2. The upper portion of the lower ladder is provided with a first roller and an upper fixing portion above and below, while the lower portion is provided with a second roller and a lower fixing portion above and below the lower ladder. A lower part is provided with a third roller and a fourth roller on the upper and lower sides, and one end of the operating rope is fixed to the upper fixing part, while the other end of the operating rope is from the third roller to the first part. The expansion / contraction ladder with the operation rope slack prevention mechanism according to claim 1, wherein the expansion / contraction ladder with the actuation rope sag prevention mechanism is fixed to the lower fixing portion via the second roller, the second roller, and the fourth roller. 3. An expandable ladder in which an upper ladder and a lower ladder are slidably expandable and contractible, and an engaging means for engaging with a suspension wire is provided on an upper part of the ladder, wherein the engaging means is provided on the upper ladder. It consists of a hook part provided on the upper part and a lock mechanism that prevents the hook part from coming off the suspension wire.One end of an operating rope for releasing the locked state is attached to the end of this lock mechanism. The other end of the rope is fixed via an elastic body to a fixing portion provided at the lower part of the upper ladder via a lower roller provided at the lower part of the lower ladder and an upper roller provided at the upper part. A telescopic ladder with a mechanism for preventing the operation rope from sagging. 4. The first roller and the second roller are provided on an inner side surface of a column portion of a lower ladder, and the third roller is provided.
2. The roller and the fourth roller are provided on the inner side surface of the column portion of the upper ladder, and the upper roller and the lower roller are provided on the outer surface of the column portion of the lower ladder. An extendable ladder with a mechanism for preventing the operation rope from sagging according to item 2 or 3.