EP2836337B1

EP2836337B1 - Failure safety device in a tool holding arm

Info

Publication number: EP2836337B1
Application number: EP12874353.1A
Authority: EP
Inventors: Robin McGOUGAN
Original assignee: Atlas Copco Industrial Technique AB
Current assignee: Atlas Copco Industrial Technique AB
Priority date: 2012-04-13
Filing date: 2012-04-13
Publication date: 2018-10-10
Anticipated expiration: 2032-04-13
Also published as: EP2836337A4; EP2836337A1; WO2013154480A1

Description

The invention relates to a torque arm for holding a power tool. In particular, the invention is related to a failure safety device in such an arm.

Background

Hand held power tools such as nutrunners, screwdrivers or the like are widely used in construction industry such as the car or air craft industry.
Often, a torque bearing arm, i.e. a torque arm is arranged to cope with the torque induced during operation of the power tool. The hand held power tools are arranged at a first end of a torque arm, wherein the opposite second end of the torque arm is arranged on a fixture in the roof or on the wall adjacent a dedicated work spot of the power tool.
The torque arm is often completed with a weight compensating system including a wire that is attached to the first end of the torque arm or to the tool itself. The weight compensating system is arranged to level out the weight of the power tool, in order to further reduce the efforts of handling the power tool for the tool operator. An example for a torque arm can be found in US 2 212 695 A . Conventionally, torque arms have been made of metal and preferably the torque arms have been made of light weight metals such as Aluminium. Aluminium is preferred due to its outstanding corrosion properties and due to its light weight.
Recently, torque arms made of a fibre reinforced polymer, such as carbon fibre, have been introduced on the market. An advantage of such a composite material is that it is both light and rigid. A concern related to such material is however that it has a low ductility, compared to metals. Hence, as a consequence, in the event that such a torque arm would break, due to overload or heavy wear, it may rupture in a clean break, wherein the power tool and/or part of the torque arm could start to rotate uncontrollably as a consequence of the rupture. Further, the rupture may occur very sudden, often without apparent indications that a rupture is about to take place. A rupture of the torque arm may lead to material damages and, in a worst case scenario, personal injuries on the operator and/or other persons in the vicinity of the dedicated work spot of the power tool. Hence, in order to assure that such scenarios are avoided, there is a need for a failure safety device.

Summary of the invention

An object of the invention is to provide a failure safety device that minimizes the risk that the torque arm breaks clean off and endangers the personal security of the operator and others. This object is achieved by means of the invention according to the appended claims.
The invention relates to a torque arm for holding a power tool, the torque arm having a connection end for connecting the torque arm to a hand held power tool. The torque arm includes an outer tubing of a fibre reinforced polymer and an inner tubing of a metal material, wherein the outer tubing is adapted to withstand normal operational forces, and wherein the inner tubing is arranged inside the outer tubing as a safety measure in order to avoid a clean break of the torque arm if the outer tubing would be damaged or overloaded to such an extent that a rupture may occur.
In this application the term normal operational forces is intended to signify the magnitude of forces in terms of bending and stress that will appear during normal operation. Further, the outer tubing is arranged to take operational forces by itself. The inner tubing is primarily arranged inside the outer tubing as a safety measure in order to avoid a clean break of the torque arm if the outer tubing would rupture.
Preferably the outer tubing is made of a carbon fibre reinforced polymer, and preferably the inner tubing is made of aluminium or an aluminium based alloy.
The torque arm is a telescopic torque arm including a torque arm as described above. The telescopic torque arm comprises at least two telescopic tubular arm members of different diameters, the diameters of a relatively larger and smaller arm member being such that an innermost member is allowed to slide within the relatively larger member, wherein at least the innermost arm member of the telescopic torque arm is a torque arm as defined in any of the preceding claims, i.e. comprising an outer tubing of a fibre reinforced polymer and an inner tubing of a metal material.
The innermost arm member is provided with both a connection end for connecting the torque arm to a hand held power tool as well as a connection interface for connecting the innermost arm member to a weight compensating device adapted to be arranged vertically above the telescopic torque arm in order to compensate for the combined weight of the power tool and the innermost arm member.
In one specific embodiment the connection interface for connecting the innermost arm member to the weight compensating device includes a threaded portion arranged on the inside of the inner tubing.
The connection end for connecting the telescopic torque arm to a hand held power tool is provided on a first end of the innermost arm member and the connection interface for connecting the innermost torque arm to a weight compensating device is provided on a second end, which is opposite to the first end.
The invention also relates to a torque arm system, including a torque arm as described above. The system includes a weight compensating device with a weight carrying wire attached to the connection interface of the innermost arm member.
Further objects and advantages of the invention will appear from the following specification and claims.

Short description of the drawings

In the following detailed description reference is made to the accompanying drawings, of which:

Fig. 1 shows a telescopic torque arm according to a first embodiment of the invention;
Fig. 2 is a sectional view of a portion of the innermost arm member of the telescopic torque arm as shown in the encircled part II of fig. 1;
Fig. 3 shows a telescopic torque arm according to a second embodiment of the invention;
Fig. 4 is a sectional view of a portion of the innermost arm member of the telescopic torque arm as shown in the encircled part IV of fig. 3.

Detailed description of embodiments relating to the invention

In fig. 1, a telescopic torque arm 10 according to a specific embodiment of the invention is shown. The telescopic torque arm 10 comprises three tubular arm members 11, 12 and 13. A first outer arm member 11 of the three tubular arm members is fixed to a torque arm fixture 14 in a roof or a wall in the vicinity of the dedicated work spot of a power tool 16. The power tool 16 is fixed to the innermost tubular arm member 13, via a connection part 27, in the form of a clevis, and a tool fixture 15. The connection part is attached to connection end 28 of the innermost tubular arm member 13 by means of adhesive, screws or bolts or a combination thereof.
An intermediate tubular arm member 12 is arranged in between the outer arm member 11 and the innermost tubular arm member 13. The innermost tubular arm member 13 is arranged to slide inside the intermediate tubular arm member 12, which in turn is arranged to slide inside the outer tubular arm member 13.
Figure 2 shows a view of a portion II of the innermost tubular arm member 13, as indicated in figure 1. In figure 2 the innermost tubular 13 arm member is shown in a sectional view.
As is apparent from the figure, the innermost tubular arm member 13 comprises two adjacent and integrated tubings 17 and 18; an inner tubing 17 and outer tubing 18. The outer tubing 18 consists of a fibre reinforced polymer, preferably a carbon fibre material. The polymer may be any conventional polymer, such as e.g. epoxy, polyester, vinyl ester or nylon. The composite may contain other fibres, such as Kevlar, aluminium or glass fibres, as well as carbon fibres.
The inner tubing 17 consists of a metal, preferably aluminium or an alloy based on aluminium.
In the embodiment shown in figure 1, the clevis 27 is provided with a connection point 25, in the form of a screw hole, for connection to a weight compensating device (not shown in figures 1-2). The weight compensating device is adapted to be arranged vertically above the torque arm in order to compensate for the weight of the power tool 16 and the torque arm 10. Conventionally, such a weight compensating device comprises a wire of which a first end is held by the weight compensating device straight above the dedicated work spot of the power tool 16, and the other end is attached to the connection point 25 of the clevis 27.
In figures 3 and 4 an alternative embodiment of the invention is shown. A main difference of this embodiment with respect to the embodiment shown in figures 1 and 2 concerns the arrangement of the weight compensating device 19. As shown in figure 3, the weight compensating device 19 is arranged inside a tubular housing 28 located between the torque arm 10 and the torque arm fixture 14.
Figure 4 shows a view of a portion IV of the telescopic torque arm 10, as indicated in figure 1. In figure 4 the torque arm 10 is shown in a sectional view, such that all three arm members 11, 12 and 13 are visible.
As is further visible in figure 4, a weight carrying wire 23 connects the innermost torque arm member 13 to the weight compensating device 19. A connection interface 26 is arranged on the innermost torque arm member 13 for this purpose. In the shown embodiment the connection interface 26 is constituted of a thread on the inside of the inner tubing 17 of the innermost tubular member 13.
Further, in the specific embodiment shown in figure 4, the wire includes a hook 22 which is to be connected to a corresponding hook 21 of a fastening block 20.
The fastening block 20 comprises an outer thread that matches the connection interface 26 in the form of the inner thread on the inside of the inner tubing 17 of the innermost tubular member 13. This feature represents a further advantage of the invention. Namely, the fact that the inner tubing is made of a metal provides for the possibility to provide the innermost tubular member 13 with internal threads. On a conventional fibre reinforced polymer torque arm, without inner metal tubing, there is a very limited possibility to provide threads inside the tubular member due to the properties of the synthetic material. Also, due to the limited space inside the torque arm 10, there are limited possibilities to attach the end of the wire to the innermost tubular arm 13 at all.
Further, the connection end 28 of the innermost tubular arm 13 may be provided with inner threads on the inside of the inner tubing 17 for a connection to a connection part 27, e.g. in the form of a clevis.
As is visible in figure 4, the innermost tubular arm 13 is provided with an external bushing 24. The bushing is fixed to the innermost tubular arm 13, but is arranged to slide with respect to the intermediate tubular member 12. A similar bushing is arranged on the inside lower end of the intermediate tubular member 12, such that the outside of the innermost tubular arm 13 may slide with respect to said bushing. Further, two bushings are provided between the intermediate tubular member 12 and the outer tubular member 11. One of these bushings is fixed to the inner lower part of the outer tubular member 11 to slide with respect to the intermediate tubular member 12, and the other is fixed to the outer upper part of the intermediate tubular member 12 to slide with respect to the outer tubular member 11. Hence, when the telescopic torque arm 10 is fully extended, the bushing fixed to the outer upper part of the intermediate tubular member 12 will be in contact with the bushing on the inner lower part of the outermost tubular member 11, and the bushing fixed to the outer upper part of the innermost tubular arm 13 will be in contact with the bushing on the inner lower part of the intermediate tubular member 12.
The bushings may preferably be made of aluminium, and are preferably treated to an optimized sliding performance, e.g. by machining and the provision of a lubricant.
As is illustrated in figure 4 the gap between the innermost tubular member 13 and the intermediate tubular member 12 is wider than the gap between the outermost tubular member 11 and intermediate tubular member 12.
In the specific embodiment this is due to the fact that tubular members are readily available in specific dimensions. Hence, in order to reduce costs, the dimensions of the tubular members have been chosen from the available assortment, wherein the size and thickness of the bushings have been adapted to fit inside the available gaps. In the shown embodiment the inner bushings are therefore thicker than the outer bushings.
In a conventional process of producing tubular arm members for a torque arm the fibre material is wound around a metal rod or tube of an appropriate diameter. The fibre material is surrounded by a matrix material, e.g. the polymer. Subsequently, the product consisting of the metal rod or tube, the fibre material and the matrix material, is cured so as to homogenise and harden the fibre and matrix material and to form a composite fibre reinforced tube. In a following step, the composite tube is relieved from the metal rod or tube. This is quite a complicated and costly process in which there is always a risk that the composite tube is damaged.
In a preferred process of manufacturing the torque arm according to the invention, the innermost tubular arm member is produced by wounding the fibre material directly around the metal tubing that will eventually constitute the inner tubing. In that way the manufacturing process will be quicker and simpler and will thereby at least partly make up for the costs incurred by the provision of an inner metal tubing.
In an alternative embodiment the outer fibre reinforced polymer tubing 18 is shrinked and/or glued on to the inner metal tubing 17.
Above, the invention has been described with reference to specific embodiments. The invention is however not limited to either of these embodiments. Instead the scope of the invention is defined by the following claims.

Claims

A telescopic torque arm (10) for holding a power tool (16), which telescopic torque arm (10) comprises at least two telescopic tubular arm members (11, 12, 13), of different diameter, the diameters of a relatively larger and smaller arm member being such that an innermost member (13) is allowed to slide within the relatively larger member (12), the innermost arm member (13) of the telescopic torque arm (10) including a connection end (28) for connecting the torque arm (13) to a hand held power tool (16), wherein the innermost arm member (13) is provided with a connection interface (26) for connecting the innermost arm member (13) to a weight compensating device (19) adapted to be arranged vertically above the torque arm (10) in order to compensate for the combined weight of the power tool (16) and the innermost arm member (13), the connection end (28) for connecting the torque arm (10) to a hand held power tool (16) is provided on a first end of the innermost arm member (13) characterised in that the innermost arm member (13) includes an outer tubing (18) of a fibre reinforced polymer and an inner tubing (17) of a metal material, wherein the outer tubing (18) is adapted to withstand normal operational forces, and wherein the inner tubing (17) is arranged inside the outer tubing (18) as a safety measure in order to avoid a clean break of the torque arm (10, 13) if the outer tubing (18) would be damaged or overloaded to such an extent that a rupture may occur, wherein the connection interface (26) for connecting the innermost torque arm (10) to the weight compensating device (19) is provided on a second end, which is opposite to the first end.
The telescopic torque arm (10) according to claim 1, characterised in that the outer tubing (18) of the innermost arm member (13) is made of a carbon fibre reinforced polymer.
The telescopic torque arm (10) according to claim 1 or 2, characterised in that the inner tubing (17) of the innermost arm member (13) is made of aluminium or an aluminium based alloy.
The telescopic torque arm (10) according to anyone of the preceding claims, characterised in that the connection interface (26) for coupling the innermost arm member (13) to the weight compensating device (19) includes a threaded portion arranged on the inside of the inner tubing (17).
A torque arm system, including a telescopic torque arm (10) according to anyone of the preceding claims, characterised in that the system further includes a weight compensating device (19) with a weight carrying wire (23) attached to the connection interface (26) of the innermost arm member (13).