Rotational drive tools of the type illustrated in FIG. 1 are often referred to as ‘nutrunners’, ‘torque wrenches’ or ‘torque guns’, etc. Such tools are used in industry for tightening nuts and bolts and other similar tasks.
The tool 1 includes a handle 3 integrally moulded with a housing 5 housing a motor. A gearbox 7 is at least axially fixed to the front of the housing 5. An externally-splined tubular boss 9 forwardly projects from the gearbox 7 and a square-profiled drive member 11 projects forwardly from the boss 9. The axially-splined exterior of the boss 9 is fixed relative to the exterior of the gearbox 7 and the housing 5 and is often referred to as a serpentine.
A wide variety of attachments have been developed for this style of rotational driver, such as the reaction arm 13. The reaction arm 13 includes a portion 15 shaped to embrace and engage the serpentine of the boss 9 so that the reaction arm is restrained from rotation about the axis of the gearbox 7. Reaction arms are often axially restrained relative to the gearbox 7 via a grub screw passing axially through the serpentine-embracing portion 15 of the arm.
FIG. 3 shows the use of such a tool to tighten a nut. For this purpose, the reaction arm 13 and a socket 15 are fitted to the tool 1. The socket 15 includes a rearwardly-open square-profiled bore dimensioned to receive and be driven by the member 11, and also a forwardly-open hexagonal-profiled bore to receive and rotationally drive a nut. The assembled tool, attachment and socket set 1, 13, 15 is engaged with a nut to be tightened so that the arm 13 engages a feature fixed relative to the axis of the nut to be tightened, so that the body of the gearbox does not rotate when torque is applied to the nut. In the example of FIG. 3, the arm 13 engages an adjacent nut N.
A trigger 17 of the tool 1 is squeezable to actuate the motor to produce a rotational drive. The motor may be, for example, a mains-electric motor, a battery-electric motor, a hydraulic motor or a pneumatic motor. The gearbox receives the rotational drive from the motor and in turn rotationally drives the socket 15 via the member 11. The socket 15 in turn drives the nut.
In some applications, it is not possible or convenient to move the tool 1 into close proximity to a nut that is to be tightened. For this purpose, a variety of extension pieces have been developed. FIG. 5 illustrates an extension piece 19 including a reaction arm welded to an outer body of the extension piece. The outer body of the extension piece fits over the forward end of the tool and mates with the serpentine of the boss 9. An inner body of the extension piece is journalled to rotate within the outer body to transmit shaft power from the member 11 to a similar drive-transmitting member 11′ at the forward end of the extension 19.
FIG. 6 illustrates another extension piece 21, the outer body of which has a serpentine at its forward end, to which a reaction arm 13′ is mounted. A socket 15′ is also attached at the forward end of the extension 21. In other applications, it is not possible or convenient to coaxially align tool 1 and a nut that is to be tightened. For this purpose, various offset tools, similar to the offset tool 23 of FIG. 7, have been developed. FIG. 7 shows a gearbox 25 coupled with the offset tool 23. The offset tool 23 serves to laterally transmit rotational drive from the gearbox 25 to a hex socket 27. The axis of hex socket 27 is laterally displaced from the axis of the gearbox.
Extension pieces and offset tools and other attachments have conventionally been attached with the aid of a radially-oriented grub screw engaging the serpentine of the tool 1 as described in respect of the reaction arm 13. The present inventor has recognised that this long-accepted mode of engagement is less than entirely reliable. From time to time, various attachments have fallen off tools. This can be very dangerous. Attachments such as extension pieces 19, 21 are heavy. A falling extension piece could injure the worker operating the tool or, worse still, potentially fatally injure a worker at a lower level of a construction site. In other instances, reaction arms have axially slipped the serpentine during operation. This slippage, in the context of tools having a gearbox housing fully fixed relative to the handle, suddenly and without warning exposes the operator to the torque of the tool. This can result in strain and crushing injuries.
In various applications, it is important to know the torque applied to a driven element such as a nut. For this purpose, rotational drive tools typically incorporate some means by which the applied torque is controlled. This may entail sensors arranged to sense the torque transmitted via the member 11, or to sense feedback from the motor unit. The present inventor has also recognised that the conventional mode of attaching a reaction arm typically involves some degree of play between the arm and the tool, that this play can lead to misalignment between the axis of the tool and the nut (or other driven member), and that this misalignment can result in the tool applying about 15% less than the desired torque to the nut.
Instead of the grub screw, some rotational drivers incorporate circlips sitting in front of the serpentine. Circlips are considered fiddly and inconvenient, and relative to the use of grub screws offer no improvement in terms of alignment. Attaching a circlips in this way also offers a less than entirely reliable means of attachment. It is easy to inadvertently misalign a circlip so that it does not seat within its groove properly. Moreover, the inventor has observed that the mentioned misalignment can cause even a correctly installed circlip to conically deform and forwardly escape its groove. Of course, such circlip arrangements are incompatible with many attachments such as the extensions 19, 21.
It is not admitted that any of the information in this patent specification is common general knowledge, or that the person skilled in the art could be reasonably expected to ascertain or understand it, regard it as relevant or combine it in any way before the priority date.