Selection criteria
5.
224
Ref.1912
DDS
HARDWARE
· 204 ·
Third motor pre-selection
Calculation of the acceleration torque and time
The required acceleration torque is determined by the total inertia to be
moved and the needed acceleration.
The required acceleration is determined by the acceleration time t
AC
which
is the time estimated for the motor to reach its rated speed from zero rpm.
Taking the value of t
AC
from the equation:
Calculation of the needed rms torque Mrms
The third and last motor selection requires a new data, the RMS torque.
where:
The typical values for t
AC
, tp and tc in machine tool cycle are:
Calculation of the motor peak torque Mpeak
The required maximum torque is the sum of the friction, weight and
acceleration torque.
For a given acceleration time, we will need specific acceleration torque and
maximum torque. The motor must be able to provide a peak torque equal to
or greater than the calculated maximum torque.
n
N
Rated motor speed .
t
AC
The time it takes the motor to go from 0 rpm to the rated speed.
M
ACCELERACION
J
TOTAL
2 n
N
60 t
AC
-------------------
=
t
AC
J
TOTAL
2 n
N
60 M
ACCELERACION
----------------------------------------------------------------
=
M
RMS
M
F
M
W
M
AC
++
2
t
AC
T
----------
M
F
M
W
+
2
t
p
T
-----
M
F
M
W
M
C
++
2
t
C
T
------
++=
t
AC
acceleration time.
tp
tool positioning time.
tc
Cutting time in a machine cycle.
t
C
T
------0.6=
t
P
T
----- 0 . 4=
t
AC
T
----------
0
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