Ergonomics - Atlas Copco

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the object, the shape of the object’s cross-
section and the type of grip. For power
gripping an object with a round cross-section
and an optimal diameter (about 38 mm for
males and 34 mm for females), the maximal
gripping force capacity is, on average, 500 N
for men and 350 N for women, respectively.
Considering the tendency of the hand
to slip on the handle of a tool, these force
limits, combined with the size and surface
condition of the handle, can be used to
determine the maximal thrust force and
rotational torque for a cylindrical tool, e.g.,
a straight screwdriver.
The maximal thrust force that can be gen-
erated using the maximal gripping force can
be calculated using the following formula:
Maximal thrust force =
Maximal gripping force · µ
Where µ is the coefficient of friction
which ranges from 0.10 to 2.22, depend-
ing on the texture of the handle’s surface,
material properties, environmental condi-
tions such as temperature and lubrication.
Depending on the coefficient of friction,
the maximal thrust force varies from 50 to
1,100 N for men (maximal gripping force
500 N), and 35 to 750 N for women (maxi-
mal gripping force 350 N). These figures can
be compared with the maximal ulnar push-
down force force (75 N for men and 50 N for
women in sitting work) given in Table 3.2.
In most handle designs (handle friction), the
forces from the hand-arm system are the
limiting factors, and not the grip itself.
In the same way, variation in the maxi-
mal rotational torque can be calculated using
the variation in the friction coefficient.
Triggering
Several types of trigger are available. The
most common are the finger trigger, the
lever trigger and the thumb trigger. To
evaluate the finger trigger it is necessary
to know which finger or fingers are used. If
one finger is used, use the MVC capacity for
that finger. If several fingers are used, for
example on a level trigger, add the MVC for
the respective fingers together.
When a lever trigger is operated with
the palm of the hand, such as on a standard
grinding machine, the feed force and the trig-
ger force are applied in the same direction.
However, trigger forces exceeding 30% of the
average feed force are not recommended. The
same general rule applies to thumb triggers
Sitting postures Men Women
Grip force 500 350
Table 3.4 Maximal Voluntary Contraction
values for grip force.