Free duty cycle
A free duty cycle defines the curve of the motor speed and the torque over time.
n Speed T Cycle time
M Torque Δt
i
Time interval
t Time
Figure 3-10 Example of free duty cycle
Procedure
Determine the required motor torque as follows:
● Define a load torque for each time slice. Also take the average load moment of inertia and
motor moment of inertia into account for acceleration operations. If required, take a frictional
torque into account that opposes the direction of motion.
● With mounted gearbox:
Determine the load torque and the acceleration torque that must be supplied by the motor.
Take the gear ratio and gear efficiency into account.
Note
A higher gear ratio increases positioning accuracy in terms of encoder resolution. For any
given motor encoder resolution, as the gear ratio increases, so does the resolution of the
machine position to be detected.
The following formulas can be used for duty cycles outside the field weakening range.
For the motor torque in a time slice Δ
t
i
the following applies:
WR0L
0
*
WV/DL
L
WV/D
W
s
/DL
L
t
V/DL
5
*
M J J
n
t
i J
n
t
M M
i
=
+ •
2
06
• • +
(
•
2
06
• + +
)
•
1
•
)(
The motor speed is:
The effective torque is obtained as follows:
The average motor speed is calculated as follows:
=
+
2
•
n
n n
t
0RWPLWWHO
0RWL$0RWL(
L
T
Configuring
3.3 Configuring the motor
SINAMICS S210 servo drive system
Operating Instructions, 12/2017, A5E41702836B AA 49
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