Inertia Estimator - Siemens SINAMICS S120 Function Manual

7.12

Inertia estimator

Features
Note
This function has only been released and can be activated for drives with servo control. The
description is also valid for linear motion (torque -> force, moment of inertia, inertia -> mass,
speed -> velocity)
The "inertia estimator" function is required when the moments of inertia of the drive change
(e.g. when using tools with different moments of inertia). For this situation, continuously
repeating the motor data identification would be too complex.
For encoderless operation, the total moment of inertia of the motor and driven machine must
be known. In controlled operation (for speeds less than p1755) in the acceleration phase, it
is not permissible that the motor stalls. In closed-loop operation (speeds above p1755), the
speed/torque precontrol requires the precise moment of inertia in order to optimize the
dynamics of the speed controller. An incorrect moment of inertia at the end of the
acceleration phase, results in an undesirable overshoot or undershoot.
You can also activate the inertia estimator during operation with or without an encoder. For
operation with encoder, the moment of inertia is only included in the motor control when the
speed/torque precontrol has been activated (p1402.4 = 1).
Description
The inertia estimator only returns the correct total moment of inertia if the load does not
change during the acceleration phases.
In phases where machining takes place during the speed setpoint change, e.g. thread
cutting, the inertia estimator can be frozen via a BICO switch (source of p1502 = 1). This
means that a previously moment of inertia that was correctly determined is not modified as a
result of an incorrect estimation.
The moment of inertia is determined from the motor torque, the load torque and the speed
change and processed. For initial adaptation, the system waits for specific dead time (2 ms)
so that mechanical transients do not falsify determination of the total moment of inertia. For
operation without encoder, the total moment of inertia can only be determined in the
controlled range, because the required actual speed value is only available here.
In operation with encoder, the moment of inertia estimation operates over the complete
speed range. However, in all cases, only during sufficient torque change in the control
behavior (acceleration torque > p1560 * p0333|) and if the value of the moment of inertia
estimation is not frozen with p1502[0...n] = 1. The start value of the moment of inertia
estimator is the parameterized moment of inertia (p0341 * p0342 + p1498).
Drive functions
Function Manual, (FH1), 01/2013, 6SL3097-4AB00-0BP3
Function modules
7.12 Inertia estimator
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