Siemens Sinamics S120 Function Manual page 425

Description
If an unknown load is present during the speed change, then the moment of inertia cannot
be determined. The complete actual motor torque is known. It is not known what percentage
is used to accelerate the motor and what is used to accelerate the load. This is the reason
that acceleration or deceleration (using the speed setpoint) must be without load.
In phases where machining takes place during the speed setpoint change, e.g. thread
cutting, the moment of 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.
Phases are required in which the speed is adjusted without load. The moment of inertia is
determined from the motor torque and the speed change and is subsequently processed.
For initial adaptation, the system waits for specific deadtime (100 ms) so that mechanical
transients do not falsify determination of the overall moment of inertia. For operation without
encoder, the total moment of inertia can only be determined in the controlled range. The
required speed actual value can only be determined in the controlled range.
In operation with encoder, the moment of inertia estimation operates over the complete
speed range. However, in all cases, only during a sufficient speed change in the control
behavior (|r1518[1]| > 0.05*|p1538 – p1539|) – 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 * p0341 + p1498). The moment of
inertia estimation must be set to the highest expected moment of inertia, so that when
accelerating for the first time in the open-controlled range, the motor does not stall. As long
as the pulses are not deleted, the actual estimated value of the moment of inertia is always
used in the motor model. This value is stored in r1493. The estimated moment of inertia is
reset to the parameterized value with each pulse inhibit. The speed controller is not adapted
to the estimated moment of inertia.
Commissioning
To activate the moment of inertia estimator, set
● p1400.18 = 1
● r0108[axis number - 1].10 = 1.
A data set changeover can be used to activate or deactivate the moment of inertia estimator.
For operation with encoder, p1402.4 = 1 must also be set. If the function for adapting the
moment of inertia via BICO technology (p1497 connected) is activated, the moment of inertia
estimator is not active.
The speed setpoint change to determine the moment of inertia estimator should be realized
without load. To do this, a measuring time of at least 100 ms is necessary. After this, the
load can be connected. The estimated moment of inertia can be monitored in r1493.
If the speed setpoint changes must be realized under load, then freeze the currently
estimated moment of inertia for this time by setting the source of p1502 = 1.
Drive functions
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Function modules
7.13 Moment of inertia estimator
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