Ergonomics - Atlas Copco

WEIGHT
When grinding on horizontal surfaces, the
weight of the tool means that lower feed
forces are required. However, we never add
unnecessary weight to the designs. The
evaluation diagram gives a score of 15 for
the weight of 3.8 kg.
EXTERNAL LOAD
Typical loads for grinding machines are sel-
ected from Table 3.9 (page 81) in the chap-
ter on external load. Since the GTG 40 is a
powerful pneumatic angle grinder, it can be
estimated that the feed force is at the higher
end of the given spread. In this evaluation
feed force is estimated to be 90 N. According
to chapter 3, 70% of the feed force is provided
via the support handle. The force acting on
the support hand is therefore 63 N.
Assuming the front of the grinding wheel
is in contact with the surface, ulnar flexion
torque on the support hand can be calcu-
lated. It will be 90 mm times 63 N, 5.7 Nm.
TEMPERATURE
Expanding compressed air in the turbine
lowers the temperature of the exhaust air
which, in turn, lowers the temperature of
the machine housing. The support handle is
plastic to prevent the low temperature from
being transmitted to the operator’s hand. A
plastic spacer isolates the throttle handle
from the machine housing.
Evaluation using the method suggested
in the chapter on temperature gives a handle
temperature of 20ºC and, thus, a score of 1.
SHOCK REACTION
The only event which can cause a shock
reaction when grinding is a jammed cutting
wheel. This shock is, however, relatively
minor. Thus, shock reaction does not apply
for grinders.
Force/Torque MVC Safety factors Reduced Real load Real / Score
N/Nm Speed Frequency Duration MVC N/Nm Reduced
Trigger 380 N a1=1 a2=0.6 a3=0.5 114 N 16 N 0.14 1
Push down
straight arm 600 N 180 N 63 N 0.35 3
Ulnar fl exion 15 Nm 5 Nm 5.7 Nm 1.1 26
Table 4.2 Evaluation of external load for the grinder GTG40 F085.
VIBRATION
At the design stage, the dynamic proper-
ties of the machine in a state of imbalance
Total score: 30
135