Fagor DDS - Page 209

Selection criteria
SELECTING CRITERIA
Selection of the synchronous motor and its associated drive
5.
209
DDS
HARDWARE
Ref.1310
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 M
RMS
The third and last motor selection requires a new data, the RMS torque.
where:
The typical values for t
AC
, t
p
and t
C
in machine tool cycle are:
Calculation of the motor peak torque M
PEAK
The required maximum torque is the sum of the friction, weight and accel-
eration 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.
Verify that the motor chosen in previous selections meets the following
condition:
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

M
t
AC
t
P
t
C
t
AC
t
T
t
S
M
MAX
M
F
M
W
M
AC
++=
Peak torque equal to or greater than the calculated max. torque:
M
PEAK
M
MAX

Rated torque equal to or greater than the calculated RMS value:
M
RATED
M
RMS
