Ergonomics - Atlas Copco

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The trigger is either operated by the
thumb or by the index finger depending on
the design of the tool.
Straight chipping hammers normally have
triggers operated by more than one finger.
Normal use of chipping hammers does
not involve fast movements. Frequency is less
than 6 times per minute and duration more
than 10 seconds per operation. Riveting ham-
mers are often used with frequencies higher
than 6 times per minute and the duration of
the operation is less than one second.
Total duration can vary a lot. Try to find
the real total duration for the workplace
being analysed. If that is not possible, use
the values in Table 3.10.
Screwdrivers
The important forces are
torque from the tightening, the feed
force, and the trigger force.
For straight tools the force from the
tightening torque is experienced as a wrist
dorsal-flexion torque. It is transferred to the
hand as friction between the hand and the
tool surface. For surfaces with low friction
the grip-force can be the limiting factor. The
maximal torque that a given grip-force can
transfer can be calculated as the grip-force
times the coefficient of friction times the
diameter of the handle.
Normally the wrist’s ability to handle the
torque is the limiting factor.
For certain types of screws, e.g., self-tap-
ping screws, a considerable amount of feed
force might be needed. For those cases the
grip-force can be the limiting factor for the
feed force. Trigger forces are normally low
and distributed over several fingers.
For pistol grip screwdrivers tightening
torque, weight distribution, feed force and
trigger forces should all be taken into ac-
count. Tightening torque is experienced as a
supination torque in the wrist.
Bad 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. This
torque might be a problem while the tool is
moved to and from the bolt.
Force and torque from the feed force is
assessed as for drills.
Trigger force is normally handled with
the index or long finger.
Normal use of screwdrivers involves
fast movements. Frequency 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. The number of
screws multiplied by the duration, i.e., time