Ergonomics - Atlas Copco

Evaluation of
shock reaction
There are no standards for the evaluation
of shock reaction. The standard ISO 6544
describes a procedure for measuring the
impulse from a machine with the handle
supported. Current knowledge cannot tell
us how many shocks an operator can be
exposed to before they pose a risk.
As mentioned earlier, the shock reaction
depends on the impulse entering the machine
during the tightening sequence. Since every
tool has a torque range, the shock reaction
Torque (Nm)
M T
t u
t d
Time (s)
Fig. 3.12 A typical tightening sequence. The area
under the curve represents the impulse.
lm
will vary with the torque setting, for the same
joint characteristics. The subjective perception
of the torque reaction will also vary according
to the work posture. The evaluation proce-
dures must be very simple to be practical.
We suggest that the scaling factor is directly
proportional to the impulse measured in
accordance with ISO 6544 for the hard joint.
In most cases, the soft joint used in the
standard gives a tightening time in excess
of 300 ms and, according to our definition,
this is not a shock.
The other reason for selecting the hard
joint is that requests for information about
impulses from tools working on this joint
are received from time to time, particularly
from the automotive industry. Many manu-
facturers and users have access to this joint
and can perform measurements. In other
words, there are data available.
At the beginning of this chapter it was
mentioned that the operator’s perception of
the shock will be worse when the joint gets
softer, and for medium-soft joints his or her
perception will be more positive again.
Using the hard joint we will be unable to
find the worst joint for each torque setting.
However, when comparing different
tools at different joints, the one with the
lowest impulse will always be preferred.
Three functions are used to evaluate the
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