Ergonomics - Atlas Copco

1.5 m/s 2 . For a grinding machine with a rigid
mass loaded support handle, readings were
down to around 0.5 m/s 2 . We decided, how-
ever, to provide the machine with a lighter
plastic handle, thus saving 0.4 kg in weight.
Isolation of vibration with
a dominant direction
When designing this type of percussive
hand tool, one of the tasks is to develop
a damping system that can transfer high
feed forces over a soft mass spring system.
One source of vibration is the forward and
return action of the impact piston. This
action causes alternating pressures on the
front and rear parts of the piston, with cor-
responding oscillating reactionary forces
on the machine housing.
The isolation built into the machine
also has to be soft. The impact frequency
for these tools often lies around 30 Hz,
therefore the isolation system must have
a natural frequency of its own that is well
below this frequency.
The mass of the machine cannot be in-
creased too much without adversely affect-
ing the design, therefore the spring must be
soft. The damping system on Atlas Copco
Fig. 3.17 Analysis of the grinder in running mode as seen from the front end. Above left: the
machine is fitted with a stiff handle moving in phase. Below left: the machine is fitted with an
anti-vibration handle moving out of phase. The question is, which solution is the best?
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