Moment Of Inertia Estimator; Introduction - Siemens SINAMICS S120 Function Manual

8.12

Moment of inertia estimator

8.12.1

Introduction

Features
The "Moment of inertia estimator" function is required when the moments of inertia of the
drive change considerably during operation (e.g. when using tools or workpieces with
different moments of inertia). For this situation, continuously repeating the rotating motor
data identification to determine the moment of inertia would be too complex, or impossible on
a machine. For servo control, the "Moment of inertia estimator" is also required for the
"Online tuning (Page 120)" function.
Moment of inertia precontrol (Page 588) can be configured for vector control. This is
especially advantageous for applications, where the moment of inertia cannot be calculated
as a result of a constant motor speed.
Note
The description is also valid for linear motion (torque -> force, moment of inertia -> inertia,
speed -> velocity)
You can also activate the moment of inertia estimator during operation with or without an
encoder.
Operation without encoder:
● For operation without encoder, the total moment of inertia of the motor and driven
machine must be known.
● In controlled operation without encoder (for speeds less than p1755) in the acceleration
phase, it is not permissible that the motor stalls because of moment or inertia that has
been parameterized too small.
● In controlled operation without encoder (for speeds above p1755), the speed/torque
precontrol requires the precise moment of inertia in order to achieve the optimal speed
controller dynamic response. An incorrect moment of inertia at the end of the acceleration
phase, results in an undesirable overshoot or undershoot.
Operation with encoder
● For operation with encoder (without online tuning), the moment of inertia is only included
in the motor control when the speed/torque precontrol has been activated (p1402.4 = 1).
● For servo control with encoder (with online tuning), the relevant controller parameters for
the speed and position controller are set automatically. The automatic calculation of the
controller parameters also depends on the estimated moment of inertia.
Drive functions
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
Function modules
8.12 Moment of inertia estimator
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