WO1995011366A1

WO1995011366A1 - An apparatus for securing a ladder rung to a ladder rail

Info

Publication number: WO1995011366A1
Application number: PCT/FI1994/000476
Authority: WO
Inventors: Hannu Vainio
Original assignee: Blue Steel Oy
Priority date: 1993-10-22
Filing date: 1994-10-21
Publication date: 1995-04-27
Also published as: AU7994894A; FI934683A; FI934683A0

Abstract

The apparatus comprises guide rollers (3a, 3b), forcing tools (4a, 4b) as well as press halves (7a, 7b) for a rung (6) to be secured, to which press halves are connected powered actuators (8a, 8b). The location of a ladder blank is determined in the lateral direction with respect to the forcing tools (4a, 4b) by means of the press halves (7a, 7b) in such a way that the powered actuator (8a) of the half (7a) is placed in its extreme position and the weaker powered actuator (8b) of the press half (7b) guides the half (7b) against the other half (7a). Correspondingly, a cell inductive in the longitudinal direction detects the rung and stops the motion in the longitudinal direction of the belt. Subsequently, the forcing tools (4a, 4b) force the rung (6) close to the rail of the ladder blank (2) by bending the material of the rung away from its longitudinal centre line and form rivet-like joints against the rail, which rail is supported on a shoulder formed in the rung (6) earlier.

Description

An apparatus for securing a ladder rung to a ladder rail

The invention relates to an apparatus for se¬ curing a ladder rung to a ladder rail, the apparatus comprising a conveyor belt moving a ladder blank consti¬ tuted by the rung and the rail in the longitudinal di¬ rection, a location detector for determining the loca¬ tion of the ladder blank in the longitudinal direction of the ladder blank, support means connected to be driven by powered actuators and determining the vertical direction of the ladder blank and forcing means connect¬ ed to be driven by actuators for forcing the material of the end of the tubular rung from the centre line of the rung outwards to form another shoulder at the end of the rung.

Traditionally, a rung is secured to a ladder rail by welding or by bolt-nut joints, both working methods being, however, very slow and especially the bolt-nut joint being sensitive to corrosion in the long run, which makes the ladder construction easily into a dangerous whole. When the ladder rung is welded to the rail, the trace of welding is also very sensitive to corrosion. Further, ladders manufactured of iron mate¬ rial are very heavy and difficult to handle. When alu- minium is used as basic material, ladders manufactured are usually lighter than similar ladders manufactured of iron or its derivatives, but the traditional problem is, however, how to join a rung of aluminium to a rail of aluminium. When a bolt-nut joint is used, an electro- chemical corrosion pair is formed between aluminium and iron, which increases the corrosion of the bolt-nut pair, and accordingly, it is not advisable to use them in a ladder construction. Further, it is very difficult to weld aluminium and no automatic welding devices or robots can be used for that purpose, but the work has to be done by human labour in order to provide a steady welding. The manufacture will then be an expensive pro¬ cess.

German Publication 2800079 discloses an appa- ratus for expanding the end of a tubular piece. However, the apparatus in question is intended for small tube sizes and to be used on mounting site and it is operated by muscular strength. Further, the apparatus can be used for riveting a tube, but it is very difficult to work with and cannot be used for riveting tubes in series production.

Swedish Publication 7 614 668-7 describes an apparatus for securing a ladder rung to a ladder rail by riveting. In the apparatus disclosed in the publica- tion, the ladder rail, being a beam with an I-shaped cross-section, is positioned between press jaws, and at the same time, the ladder rung is guided by means of said jaws through a hole made in the rail to a right place. Simultaneously, a fan-shaped forcing jaw is pushed into the tubular rung, small shoulders being formed on both sides of the rail when the jaw is opened. Subsequently, it is proceeded to a second stage of oper¬ ation, at which the ladder rung is secured at a shoulder remained between the rails to a chuck similar to a dril- ling machine. A tubular or bar-shaped fitting part is pushed into the tubular rung, the purpose of the fitting part being to support the rung, when it is riveted, at the shoulders described above. In a riveting situation, the chuck similar to a drilling machine forces the shoulder of the rung to sink against the rail, and at the same time, an anvil on the other side of the rail expands the other end of the rung against the rail. Drawbacks of the apparatus are its complicated structure and special structures of its riveting tools. According- ly, the apparatus is very sensitive to failure. More- over, it shall be noted that it is difficult and very complicated to service the apparatus and to maintain the riveting tools.

The object of the present invention is to pro- vide an apparatus for securing a ladder rung and a lad¬ der rail to each other. This object is achieved by the apparatus according to the invention, which is charac¬ terized in that the first support means supporting in the vertical direction of the rung is a support means moving to a predetermined position and that the second support means moves against the first support means in such a way that the support means align the centre line of the rung into a line passing substantially through the forcing means. An essential idea of the invention is that lad¬ der rails are positioned against shoulders in a ladder rung, and then the ladder blank is moved to an appara¬ tus, in which the rung is supported between the shoul¬ ders by support means, and subsequently, both ends of the rung left free are forced simultaneously by means of tools of the apparatus in such a way that the rail remains between the shoulders at the end of the rung. Another essential idea of the invention is that a double shoulder is provided from a tubular blank by means of a simple tool, and consequently, this shoulder is strong and not torn at its edges. A further essential idea of the invention is that one of the movable support means acts as a working level, against which the rung is pressed between its shoulders by the second support means.

The apparatus described above is very reliable in operation and simple and does not need continuous service. The forcing tools of the apparatus wear very little, which keeps the tool costs low as well. Further, the working process is very quick and thus the degree of utilization of the ladder line very high. Moreover, the rail and the rung are secured to each other at one stage of operation, and it is not necessary to move the ladder blank from one machine to another. The invention will be described in more details in the following drawings, in which

Figure 1 shows an apparatus for securing ac¬ cording to the invention simplified and

Figures 2a to 2c show the progress of a secur- ing procedure by means of the apparatus according to the invention.

Figure 1 shows an apparatus for securing 1, which apparatus comprises a conveyor belt not shown in the figure in more detail, the belt moving a ladder blank 2 from below and operating in a generally known manner, guide rollers 3a and 3b keeping the ladder blank in the vertical direction, forcing tools, i.e. forcing means 4a and 4b, moving in their cylinders 5a and 5b by means of powered actuators, which may be power units known per se based on hydraulics, pneumatics or the like. The forcing tools 4a and 4b are attached by means of the cylinders 5a and 5b as well as the powered actua¬ tors to the frame of the apparatus for securing 1, which frame is not illustrated in greater detail in Figure 1. The apparatus for securing 1 further comprises support means for a rung 6 to be secured, i.e. press halves 7a and 7b, which move by means of powered actuating de¬ vices, i.e. powered actuators 8a and 8b, according to guides fastened to the frame of the apparatus for se- curing 1. The powered actuators 8a and 8b are further attached to the frame of the apparatus for securing 1. Before securing process, the ladder blank 2 is posi¬ tioned on the conveyor belt in such a way that in ready- made holes of the lowest rail is mounted a rung sup- ported on its shoulders in the vertical direction in such a manner that also the highest rail may be posi¬ tioned to be supported on the shoulders of the other end of the rungs. Subsequently, the ladder blank 2 is guided between similar guide rollers 3a and 3b to the apparatus for securing 1, in which the ends of the rails are aligned by driving the ladder blank against a plane sur¬ face. Since the distance between the rail ends and a first securing point is equal to the distance between the forcing tools and the plane surface, the location of the ladder blank in the longitudinal direction is accurately determined. Subsequently, the press halves 7a and 7b of the rung 6 to be forced can be enclosed around the rung 6, whereby the location of the ladder blank is accurately determined also in the lateral di- rection. The halves 7a and 7b are moved in such a way that the stronger one of the powered actuators 8a and 8b moving the press halves is at first driven to its predetermined limit value. Then the rung 6 and at the same time the ladder blank 2 are pressed by the press half having the weaker powered actuator close to the other press half, whereby the stronger powered actuator with its press half acts as a working level and does not move. After this, the forcing tools 4a and 4b force the rung 6 close to the rail of the ladder blank 2. Upon forcing, the tools 4a and 4b are removed from their positions and the press halves 7a and 7b are opened by the powered actuators 8a and 8b. The ladder blank is moved in the direction of arrow A along a desired dis¬ tance, until next rung to be forced is at the tools 4a and 4b. The moving distance can be sensed for instance by different sensing cell solutions, which detect the next rung and stop it at the right place. Tachometric connection can be used for detecting, which is known per se as well and will not be discussed any further in this connection. Figure 2a shows a situation when an alignment point 9 of the forcing tool 4a is inside the rung 6 to be forced. Figure 2a also shows a shoulder 10, against which the rail 11 is supported at the assembling stage. Figure 2b shows a situation when the forcing tool 4a presses the end of the rung 6 against the press halves 7a and 7b. Then part of the rung 6 above the rail 11 bulges out from the alingment point 9 outwards. The alignment point 9 acts at the same time as a support for the rung 6, and accordingly, the rung 6 cannot yield elsewhere than at desired place.

In Figure 2c, the forcing tool 4a has pressed another shoulder at the end of the rung and the rail 11 has thus remained between two shoulders and stays steadily in place. It shall be noted that the just-made shoulder is double and thus unbreakable at its outer edge and very stable. It shall be noted further that the forcing process takes place at both ends of the rung simultaneously, due to which both rails can be secured to the rung easily enough. It shall also be noted that the rung is not able to move between the press halves, due to which its surface remains tidy and undamaged.

The drawings and the descriptions relating to them are only intended to illustrate the invention. As to the details, the apparatus for securing according to the invention may vary within the scope of the claims. So in some cases, it may be preferable to use separate roller conveyors for moving the ladder blank or forcing tools connected to eccentrics as power tools.

Claims

Claims:

1. An apparatus for securing a ladder rung to a ladder rail, the apparatus comprising a conveyor belt moving a ladder blank (2) constituted by the rung (6) and the rail in the longitudinal direction, a location detector for determining the location of the ladder blank (2) in the longitudinal direction of the ladder blank (2), support means (7a, 7b) connected to be driven by powered actuators (8a, 8b) and determining the verti¬ cal direction of the ladder blank (2) and forcing means (4a, 4b) connected to be driven by actuators (5a, 5b) for forcing the material of the end of the tubular rung ( 6) from the centre line of the rung (6) outwards to form another shoulder at the end of the rung (6), c h a r a c t e r i z e d in that the first support means (7a) supporting in the vertical direction of the rung is a support means (7a) moving to a predetermined position and that the second support means (7b) moves against the first support means (7a) in such a way that the support means (7a, 7b) align the centre line of the rung ( 6) into a line passing substantially through the forcing means.

2. An apparatus according to claim 1, c h a r a c t e r i z e d in that the powered actuator (8a) of the first support means (7a) has a stronger power than the powered actuator (8b) of the second sup¬ port means (7b) so that, with the first support means (7a) in the predetermined position, the powered actuator (8b) of the second support means (7b) moves the second support means (7b) to press against the substantially immovable first support means (7a) .

3. An apparatus according to claim 1 or 2, c h a r a c t e r i z e d in that the powered actuator (8a) having the stronger power is in its extreme posi- tion before the second support means (7b) connected to the other powered actuator (8b) is moved against the support means (7a) connected to the powered actuator (8a) having the stronger power.

4. An apparatus according to any of the fore¬ going claims 1 to 3, c h a r a c t e r i z e d in that the rung (6) is supported substantially over its whole surface.

5. An apparatus according to any of the fore- going claims 1 to 4, c h a r a c t e r i z e d in that the powered actuators (8a, 8b) are hydraulic cylinders.