Ergonomics - Atlas Copco

taken to tighten one screw, can be used. If
that is not possible, use the values given in
Table 3.10.
Impact and impulse
nutrunners
The important forces are weight
distribution of the tool, trigger
forces, the feed force and, for bigger
tools, the torque from the motor.
Poor weight distribution might give a
radial-flexion torque equal to the weight of
the tool times the distance from the center
of gravity to the center of the handle.
Trigger force is normally handled with
the index or long finger.
In some applications feed force needs to
be considered, e.g., applications where small
impact tools are used for self-tapping bolts.
The reaction torque acting on the han-
dle is only a small fraction of the installed
torque. The torque experienced is only
the torque from the vane motor itself. For
impulse tools this torque can be approxi-
mated as the tool’s maximum torque capac-
ity divided by 40 and for impact tools the
corresponding figure is the maximal torque
capacity divided by 120.
Normal use of impact and impulse
nutrunners involves fast movements. Fre-
quency is more than 6 times per minute and
duration is less than 3 seconds per screw
Total duration can vary considerably. Try to
find the real total duration for the workplace
being analysed. Number of screws times
the duration, i.e., time taken to tighten one
screw can be used. If that is not possible use
the values given in Table 3.10.
Angle nutrunners
The important forces are the reaction
torque from the tightening, weight dis-
tribution of the tool and trigger forces.
The reaction torque from the tight-
ening is regarded as a shock reaction
if the tightening time is shorter than
300 ms. When the tightening time ex-
ceeds 300 ms the muscles in the hand-
arm system have time to counteract and
the torque reaction is assessed as a force
acting on the hand-arm system.
In most cases where the tool is used in
a two-handed operation the force is handled
as a standing pull force in the right arm
and a slightly smaller standing push force
in the left arm. This can vary considerably,
depending on the posture required to reach
the bolt to be tightened.
Many problems relating to reaction
torque are due to the fact that reaching the
bolt requires awkward postures.
In some cases angle nutrunners are
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