Patent Application
20130256349
The present invention relates to tool tethers and tools with tethers.
There is a significant risk of hand tools being dropped while working at height. A tool weighing 0.43 kg (1 lb) when dropped from a height of 9.14 m (30 feet) will reach an impact speed of 27.36 kph (17 mph). If the distance after impact is assumed to be 0.99 cm (0.39 inches) then the tool in question will exert a force of 1320 N or mass equivalent of 134.49 kg (296.5 lb). The extent of the damage caused depends on the orientation, shape, and the material from which the tool is made of. It can cause direct or indirect injury to the work force or civilians by landing on a person or by creating floor hazards on the level below.
Potential risks to the company using a tool that is dropped include sickness absences, risk of litigation, as well as damage to property, processing equipment or the tool itself. Not only are they hazards, but falling tools can also reduce productivity by time lost in retrieving the dropped tool. According to UK Health and Safety surveys, being struck by falling objects is the second most common cause of fatal accidents to the work force.
In order to address these issues, there needs to be an attachment point on the tool for attaching it to an anchor, e.g. via a lanyard. An effective attachment point must be permanent, durable, ergonomic, must not compromise the integrity of the tool and, most importantly, must not fail in the case of a drop. Lack of existing standards and guidelines (in the UK at least) regarding how a tool should be attached to a lanyard often means that improvised, inadequate methods of arresting are used. Alternatively, many tools are used without any preventative measures, which is clearly dangerous. Many tools used in industry today are not designed with a permanent attachment point suitable for a lanyard, and this is the reason why companies improvise. Improvised attachment points can often invalidate the tool manufacturer's warranty.
When improvising an attachment point often it has often been wrongly assumed that the force involved in a drop is given by the formula F=ma. This is only valid for calculating weight and fails to take into account the change in kinetic energy (FAve×d=KEFinal−KEInitial=ΔKE).
Embodiments of the present invention are intended to address at least some of the abovementioned problems.
According to a first aspect of the present invention there is provided a tool tether including or comprising:
a plurality of strands of flexible material, and
a securing arrangement for securing the plurality of strands in a loop.
In use, the loop can be secured through an aperture in (or another loop on) a portion of a tool, typically a handle portion of the tool. The loop may be a single closed loop that can be generally circular or oval in shape.
The securing arrangement may comprise a tubular member that is compressed over portions including, or adjacent to, both ends of the plurality of strands, thereby forming and securing the loop. The securing arrangement may be formed of a deformable material/metal, e.g. aluminium. At least one further tubular member may be compressed adjacent to the first-mentioned tubular member. The tubular member may have an oval cross-section prior to the compression, and may have a generally circular cross-section following the compression. An inner diameter of the tubular member prior to the compression may be at least equal to a combined diameter of the strands. The tubular member may have dimensions selected from a set including: height: 7 mm, 8 mm or 9 mm; thickness: 1 mm, 1.2 mm, 1.5 mm; internal diameter: 2 mm, 2.5 mm, 3 mm.
The securing arrangement may surround at least a crossed-over portion of the strands. In some embodiments a portion including at least one said end of the strands protrudes out of the securing arrangement and in some embodiments portions including both ends of the strands protrude out of the securing arrangement.
The tether may further include a strand sheath that covers at least a portion of the strands. The sheath may be formed of flexible material, such as plastic, and may be of tubular form.
The tether may further include a securing arrangement sheath that covers at least a portion of the securing arrangement. The securing arrangement sheath may be formed of a flexible material, such as polyolefin, silicone, elastomeric, fluorinated ethylene propylene, polyvinylidene fluoride, fluoropolymer or polyvinyl chloride. The securing arrangement sheath may be fixed, e.g. by heat shrinking, onto the strand sheath.
The strands may be formed of galvanised steel. A said strand may have a diameter in a range of around 0.160 mm-0.330 mm. At least some of the strands may be woven/twisted together for strength. There may be around 5-10, and typically, 7 said strands in the tether. An embodiment of the tether may be intended for use with a tool weighing up to 1 kg, in which case a combined diameter of the strands may be around 1.5 mm. An embodiment of the tether may be intended for use with a tool weighing up to 1.5 kg, in which case a combined diameter of the strands may be around 2.0 mm. An embodiment of the tether may be intended for use with a tool weighing up to 2.5 kg, in which case a combined diameter of the strands may be around 2.5 mm.
In practice, the tethers can be batch tested and issued with a safety certificate. The tethers and/or the tethered tool can include a tracking device, e.g. an RFID.
According to another aspect of the present invention there is provided a tool including or comprising:
a portion including a bore or a loop;
a plurality of strands, and
a securing arrangement for securing the plurality of strands in a loop through the bore or the first mentioned loop.
The portion may include a handle portion. The portion may be located towards a tip of the handle.
The tool may be a hand tool. The tool may be powered.
A lanyard for fixing the tool/tether to a person may further be provided.
According to another aspect of the present invention there is provided a method of forming a tool tether, the method including:
forming a plurality of strands of flexible material into a loop;
securing the strands in the loop by fixing a securing arrangement over at least a crossed-over portion of the strands.
The loop may be passed through a bore in, or another loop on, a tool.
According to a further aspect of the present invention there is provided a method of testing a tool tether substantially as described herein.
Whilst the invention has been described above, it extends to any inventive combination of features set out above or in the following description. Although illustrative embodiments of the invention are described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments. As such, many modifications and variations will be apparent to practitioners skilled in the art. Furthermore, it is contemplated that a particular feature described either individually or as part of an embodiment can be combined with other individually described features, or parts of other embodiments, even if the other features and embodiments make no mention of the particular feature. Thus, the invention extends to such specific combinations not already described.
The invention may be performed in various ways, and, by way of example only, embodiments thereof will now be described, reference being made to the accompanying drawings in which:
The number and dimensions of the strands will depend on the weight of the tool with which the tether 100 is to be used. Each strand may have a diameter between around 0.16 mm-0.33 mm. Examples of preferred strand dimensions for tools of certain weights, as calculated by the present inventors, are given below:
The loop of the example tether 100 has a diameter of 8 cm, but in other embodiments, the diameter can be up to 12 cm. The combined cross-sectional thickness/diameter of the strands may be achieved in some cases by weaving/twisting around 5-10, and in one embodiment 7, strands of galvanised steel.
Below is a table (split in two) showing calculations performed by the inventors relating to the predicted results of the drop tests.
The table above relates to a tether having a diameter of 1.5 mm, but it will be understood that similar information can be derived for tethers having other diameters, e.g. 1.0, 2.0, 2.5, 3.0, 3.5, 4.5, 4.5 mm. These figures were used by the present inventors to produce guidelines for testing each tether category. The data gathered was analysed to produce the relevant probability of failure for each tether type in the category. This data corresponds to the maximum stress the tether could possibly endure:
The type of data needed for this testing can include:
The probability of failure was calculated for each and every individual test condition and with every tether category. The values were then cross referenced to draw a picture of each change to the testing parameters as to the failure rate of the tether. The probability of failure was intended not to be larger than 0.00000003 (±0.000000005) in 106. This should detect if the tether is being affected by each test condition. Once the data was collected for each category of tethers, the failure probability was cross referenced to explore if any of the test conditions showed an abnormality affecting the probability of failure (zero in one in a million). If the above value was not achieved then that category of the tether/product was not used. Further investigation, redesign, re-manufacture can be required and the necessary changes implemented. The new range then can only be reintroduced after being re-tested in line with the testing regimes and only when the above statistics have been achieved for each and every test condition.
The strands are held together in the loop formation by means of a securing arrangement 104. In the example, the securing arrangement comprises a tubular member/ferrule that is compressed over at least a crossed-over portion of the strands. During manufacture, first 102A and second 102B ends of the strand are passed through the tubular member, crossing each other within it, with portions (of around 1-3 mm in length) of the ends protruding out of the respective ends of the tubular member. A sheath 106 covers the majority of the exposed portion of the strands, generally up to the ends of the securing arrangement 106. This sheath can be formed of tubular, flexible material, such as polyolefin, silicone, elastomeric, fluorinated ethylene propylene, polyvinylidene fluoride, fluoropolymer or polyvinyl chloride.
The tubular member 104 will normally be formed of strong, deformable material, such as aluminium. After the strands have been passed through it, it is compressed and a sectional view of the result is shown in
The tether 100 is connected to the tool 300 by means of passing through a bore 304 formed in a portion of the tool. The tool in the illustrated example is a pair of pliers and the bore is formed towards the tip of one of its handles 301. The bore will have a diameter slightly greater than the portion of the tether that does not include the securing arrangement. However, it will be appreciated that the manner of attachment between the tether and the tool can be varied. For example, the bore may be located elsewhere on the tool, or a loop, shackle or the like can be fixed to a portion of the tool, with the tether being attached to that. The tether can be attached to the tool during manufacture, or can be retro-fitted to tools without suitable connection means. Although a set of pliers are shown in the Figure, it will be appreciated that the tether can be used with a wide variety of tools, including powered tools, such as drills and saws.
The inventors also developed a rigorous testing regime, including drop and tensile testing, for testing the tethers. These test results were then used to continuously improve and maximize the safety of the tethers by performing a Weibull analysis on the test results.
The inventors calculated that N=50 provided an excellent testing regime, but it will be understood that the number can vary. The testing procedures and the construction of the tethers (including the type of materials used, the number and thicknesses of the strands, and the use of the sheath(s)) described herein could be considered to be over-engineered according to conventional engineering practice. However, the inventors overcame this technical prejudice and determined that tethers that satisfied requirements that go above and beyond those of conventional safety tethers are beneficial in terms of safety and peace of mind for customers/users. In practice, the tethers can be batch tested and issued with a safety certificate. The tethers/tools can incorporate microchip technology, e.g. RFID tags, in order to make them traceable for after care maintenance.
The tethers described herein can enhance a tool's performance without compromising its integrity.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1205541.4 | Mar 2012 | GB | national |
