Siemens SINAMICS S120 Configuration Manual page 66

Configuration
5.3 Dimensioning
Load cycle
A load duty cycle defines the characteristics of the motor speed and the torque with respect
to time.
Figure 5-8
A load torque is specified for each time period. In addition to the load torque, the average
load moment of inertia and motor moment of inertia must be taken into account for
acceleration. It may be necessary to take into account a frictional torque that opposes
the direction of motion.
The gear ratio and gear efficiency must be taken into account when calculating the load
and/or accelerating torque to be provided by the motor. 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.
For the motor torque in a time slice Δ
M
The motor speed is:
The RMS torque is obtained as follows:
The average motor speed is calculated as follows:
66
Example of a load duty cycle
n
2
( )
= J + J • • • i
60 t
t
the following applies:
i
n
2
(
s
+ J • • + M
60 t
Configuration Manual, (PFK7S), Edition 12.2006, 6SN1197-0AD16-0BP1
1
)
+ M •
t
i •
n = n • i
∑
2
M • Δ t
M =
T
n + n
2
n =
t
Synchronous Motors 1FK7
• t