AU721177B3 - A ladder with hook lever devices - Google Patents

Description

APPLICANT: DOFAIR COMPANY LTD

NUMBER:

FILING DATE: Form COMMONWEALTH OF AUSTRALIA The Patents Act 1990 PETTY PATENT SPECIFICATION FOR AN INVENTION ENTITLED: A LADDER WITH HOOK LEVER DEVICES The following statement is a full description of this invention, including the best method of performing it known to me/us: -1- A LADDER WITH HOOK LEVER DEVICES BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a hook lever device on a ladder, and particularly to a hook lever device mounted on an extendable ladder for locating a movable ladder part thereof in place.

2. Description of Related Art: Usually, an extendable ladder consists of one stationary ladder part and one movable ladder part, and the movable ladder part can be move up and down with respective to the stationary ladder part. In order to locate the movable ladder part at a certain elevation after the ladder is extended, normally a fixing device such as a hook type device is provided to execute the job of locating the movable ladder part. The hook type device is installed on the movable ladder part and can be operated manually to hang up to one of the rungs on the stationary ladder such that the movable ladder part is able to remain unmoved steadily. There is another kind of hook device that can achieve the same goal without operating it manually but by means of a weight portion being provided therein. Once the movable ladder is extended out of the stationary ladder a desired length, a gravity force of the weight portion will allow the hook portion to attach onto one of the stepping bar of the stationary ladder part automatically. However, both the devices are inefficient. The manual hook device is inconvenient to operate and the weighted hook device makes the ladder is inconvenient to carry around.

SUMMARY OF THE INVENTION The present invention is to provide an extension ladder in which a hook-type fixing device has have a novel and easy operated structural arrangement such that a movable ladder part therein can be steadily located as desired.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention can be more fully understood by referring to the following description and accompanying drawings, in which: Fig. 1 is a plan view of two hook lever devices according to the present invention hooking onto one of the stepping bars of a movable ladder part; Fig. 2 is a side view of a hook lever device at left side in Fig. 1; Fig. 3 is a partial top view of Fig. 2 to illustrate parts of the hook lever device; Fig. 4 is an enlarged plan view of Fig. 2 illustrating a partition fixedly attached to a cover plate on the device; Fig. 5 is the plan view of the hook lever device in Fig. 2, illustrating a state of the movable ladder part moves upwards; Fig. 6 is a plan view illustrating a state of the movable ladder part moving further upwards; and Fig. 7 is a plan view illustrating the movable ladder part shown in Fig. 6 moving downwards.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figs.1, 2, 3 and 4, an extension ladder with hook lever device is basically comprised of a pair of two corresponding hook devices, which are fixed to a respective side wall of both rails opposing to each other on the movable ladder part Each hook device is made up of a hook bar a blocking part a cover plate a partition a spring (4) and a pivot The hook bar is a long bar with a hook shaped end with a U shape opening for hooking onto a stepping bar (71) of the stationary ladder part The hook end, which is shaped like a triangle, has a big opening and a small hook top. The other end of the hook bar is a straight end, and rotatably attached to the lateral wall of the respective rail on the movable ladder part by the pivot The blocking part is a long stick with a sharp end, and the other end thereof is split into a U-shaped fork end part. The fork end, enclosing the hook bar in between, is then pivoted at the middle of the hook bar The purpose of the blocking part is to block the hook opening of the hook bar and keep in contact with the stepping bar (71) of the stationary ladder part (7) when the movable ladder part moves downwards. The cover plate is a U-shaped plate and has a width slightly smaller than the width of the lateral wall of the respective rail on the movable ladder part Both lateral sides of the cover plate are attached to the respective rail at both extending out edges thereof located at the lateral wall. A partition plate (31) also is a U-shaped plate, and the width thereof is smaller than that of the cover plate The partition plate (31) is positioned opposing to the cover plate and attached to the cover plate An example for the partition plate (31) attaching to the cover plate is illustrated in Fig. 4. It can be seen in Fig. 4 that the partition plate (31) has four locating tabs (311) at both lateral sides thereof. The cover plate is provided with four holes corresponding to the locating tabs (311) such that the tabs (311) can be fixedly fitted with the holes. It is noted that the attachment way shown in Fig. 4 is taking an example only and other conventional ways can be adopted to achieve the attachment. A space confined between the cover plate and the partition plate (31) receives the straight end of the hook bar A pivot which provides a threaded end and a hexagonal head, passes through the cover plate at a center part thereof, the straight end of the hook bar and the partition plate Furthermore, the threaded end of pivot extends to the other side of the lateral wall so as to be fastened by a nut from an opening 80 on another lateral wall opposite to the lateral wall. A torsion spring 4 is located at a space between the partition plate (31) and the lateral wall attached by the cover plate and surrounds the pivot The spring has two extended ends, and one of the ends is hooked onto the straight part of the hook bar while the other one of the ends is hooked onto one of the corners on the cover plate Therefore, the hook bar is capable of keeping pressed by the torsion force of the spring An explanation regarding the operation of the hook lever device according to the present invention will be described hereinafter thoroughly.

Please referring to Fig. 5, initially, the hook bar is hooked onto the stepping bar (71) of the stationary ladder part as shown in Fig. 2. When the movable ladder part starts to be moved upwards, the blocking part slowly comes in contact with the lower edge of the stepping bar At the right moment, the blocking part is at the lowest rotated position, that is, the blocking part is not possible to be rotated any further downward. Therefore, as the movable ladder part continues to move upwards, the hook bar begins to rotate in the anticlockwise direction with respect to the axial axis of the pivot against the torsion force of the spring The movable ladder part then moves further upwards until the blocking part is no longer in contact with the stepping bar (71).

Referring to Fig. 6, once the blocking part (2) being no longer in contact with the stepping bar (71), the hook bar then rotates clockwise and returns to its original position under the torsion force of the spring However, at this moment, the top end of the hook bar is approaching the bottom edge of the stepping bar When the top end of the hook bar (1) comes into contact with the bottom edge of the stepping bar and obstructs the motion of the hook bar the hook bar again rotates in the anti-clockwise direction with respect to the axial axis of the pivot Once the top end of the hook bar departs from being obstructed by the stepping bar the hook bar again rotates back to its original position under the torsion force of the spring At this instance, if the movable ladder part is lowered, the hook opening of the hook bar will then hooks onto the stepping bar (72) and thus fixed the movable ladder part in place as shown in Fig. 1. It can be understood that the movable ladder part continues to move upwards, the same operation as described above will repeats until the movable ladder part is not further extended upwards.

Referring to Fig 7, once the movable ladder part is moved downwards from the state shown in Fig. 6, the blocking part is obstructed by the upper edge of the stepping bar (71) and rotates to block the hook opening of the hook bar When the hook opening is kept blocked by the blocking part the stepping bar is then kept untouched with the hook opening. If the movable ladder part continues moving downwards, the block part will then come in contact with the stepping bar block the hook opening, and prevent the hook opening from hooking onto the stepping bar Thus, the movable ladder part can then easily move from the top downwards to the lowest possible position.

In conclusion, the advantage of the present invention is the ability to move the movable ladder part up and down easily, efficiently and accurately, and the movable ladder part can be easily operated to locate at a specific elevation. When the movable ladder is moved upwards, the hook opening on the hook bar will be above a specific stepping bar on the stationary ladder part When the movable ladder is lowered to hook onto the specific stepping bar, the blocking part is below the specific stepping bar. This allows the hook opening to hook onto the stepping bar securely. Since the top part of hook end is a shape of sharp convergence, when the top part comes in *contact with the lower edge of any stepping bar, the top end can slip over them easily. Thus, the movable ladder part can be moved upwards without any difficulty. When the movable ladder part moves downwards, the blocking part (2) blocks the hook opening of the hook bar Thus, the movable ladder part can be moved downwards easily without having the hook opening being hooked onto any of the stepping bars.

While the present invention has been described with reference to a preferred embodiment thereof, it is to be understood that modifications and variations may be easily made without departing from the spirit of this invention which is defined by the appended claim.

Claims (3)

1. A ladder including:- a first ladder part with a plurality of stepping bars; a second ladder part with at least one hook bar device, the second ladder part being telescopically mounted with respect to the first ladder part to selectively alter the total height of the ladder, each of the hook bar devices including a hook bar pivotably mounted with respect to the second ladder part and adapted to engage a stepping bar of the first ladder part, a spring for urging the hook bar into engagement with a stepping bar of the first ladder part, and a blocking part pivotably mounted with respect to the hook bar for selectively preventing the hook bar from engaging a stepping bar of the first ladder part, characterized in that, when the hook bar is engaged with a stepping bar and when the ladder is loaded, the hook bar is under a tensile load such that the first ladder part and second ladder part are urged together.

2. A ladder as claimed in claim 1, wherein the first ladder part is a stationary lower ladder part and the second ladder part is a movable upper ladder part and wherein the hook bar extends upwardly from the point at which it is pivotably mounted to the second ladder part.

3. A ladder as claimed in claim 2, wherein the hook bar device further includes:- a U-shaped cover plate mounted to the wall of the side rail of the second ladder a reversed and U-shaped partition plate mounted in opposing fashion to the U- shaped cover plate so as to define a hook bar accommodating space between the partition plate and the cover plate; and a pivot bolt passing through the cover plate, the hook bar, the partition plate, and the wall of the side rail. 0 2o^