Ergonomics - Atlas Copco

EXTERNAL LOAD
When drilling, the external loads are torque
and feed force. Torque depends on the drill
speed selected. The drill selected here is a
6,000 rpm tool with a maximum measured
torque of 1 Nm. Tools with higher speeds
give lower torque. The torque is experienced
as a supination torque. For tools with lower
speeds the operator uses the left hand for
support. The chuck guard acts as an effec-
tive support grip. This tool is mainly used
in a standing posture, drilling on a vertical
surface. The higher the feed force, the faster
the rate of penetration. A typical feed force
for this tool would be 150 N.
WEIGHT
As a typical material removal tool, the drill
is not used in a highly repetitive motion.
Tool weight is 0.7 kg and the score is 3.
TEMPERATURE
Expanded compressed air from the motor is
cold. However, the full power of the tool is
rarely utilized during drilling, and the drill-
ing cycle is usually short. Normal frequency
of use lies somewhere between once every
five minutes and six times per minute. The
average period of use per day is assumed
to be one hour. It can be assumed that the
duration is 10 seconds. This results in 360
times per day or 45 times per hour. Thus, an
average drilling sequence is 3,600/45 = 80.
When the temperature at the handle is
measured, the tool should run for 10 sec-
onds at a speed equal to 75% of free running
speed, a typical load when drilling, and giv-
ing 50% power, and rest for 70 seconds.
The measured temperature is 17ºC, giv-
ing a score of 3.
SHOCK REACTION
A shock and its reaction happen during a
short space of time. Events of less than 300
ms in duration can be considered to be shocks
and, during this time, the operator can do
little to influence the course of events.
A shock may occur when the drill bit
penetrates a plate. Most of the feed force is
Force/Torque MVC Safety factors Reduced Real load Real / Score
N/Nm Speed Frequency Duration MVC N/Nm Reduced
Trigger 130 N a1=1 a2=0.7 a3=1 91 N 15 N 0.2 2
Push forward
straight arm 450 N 315 N 150 N 0.5 4
Supination 15 Nm 10 Nm 1 Nm 0.1 1
Table 4.4 Evaluation of external load for the Drill LBB 26 EPX-60.
Total score: 7
139