Ergonomics - Atlas Copco

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heavy, assembly work is often highly repeti-
tive. Work organization and work-
station design are therefore very important.
Design for good ergonomics
For the operator performing repetitive
tasks, maintaining a correct posture is of
great importance. The location of joints
and the selection of machine type must be
considered. Screwdrivers are available in
straight or pistol grip versions. Working
postures with the wrist in a natural position
are preferred.
Modern straight tools have a textured
surface that increases the friction between
the tool and the hand. This enables the oper-
ator to hold the machine without excessive
effort. Since the tools are usually light and
the tightening operation tends to make them
rotate in the hand, the operator absorbs the
reaction torque at the end of the tighten-
ing sequence. The magnitude of this kind of
shock reaction is related to the type of joint
and the function of the tool. With hard joints
and pneumatic tools with a fast clutch, the
tendency of the tool to rotate in the opera-
tor’s hand, caused by the impulse, is low.
Electric screwdrivers, on the other hand,
can be controlled so that the operator experi-
ences almost the same torque reaction, in-
dependent of joint stiffness. Thus, the
muscles in the operator’s arm are more
relaxed. For this reason, many vehicle
assembly plants permit a higher torque
before torque reaction supports are required
for electric tools than for pneumatic tools.
Screwdrivers often have a push-to-start
trigger function. Thus, the tool starts itself
when the bit is pressed against the screw.
Different screw heads require different
amounts of force to keep the bit in place.
Therefore the screw must be selected with
care to avoid excess load on the operator.
Safety
Most screwdrivers are low-powered tools and
represent a low safety risk to the operator. As
regards pneumatic tools in the upper torque
range, however, if the clutch is wrongly
adjusted, it may fail to disengage at the end
of the tightening sequence. Therefore the
clutch must always be tested before the tool
is installed at a workstation.
The air pressure along the assembly
line must be controlled and sudden pressure
drops must be avoided. If a pressure drop
occurs during tightening, the torque from the
motor may not be strong enough to disen-
gage the clutch and the operator might be
forced to absorb the reaction torque without
any previous warning. This may cause wrist
problems.