Siemens SINAMICS S120 Function Manual page 554

Function modules
9.14 Advanced Position Control (including Active Vibration Suppression)
Note
Intervention of APC in the speed control loop that can be critical for system stability
The functions integrated in APC represent their own control loop - or provide the possibility of
intervening in the speed control loop. As a consequence, parameterizing the APC is critical
from a stability standpoint.
To optimize APC in conjunction with a direct measuring system, it helps to have a deeper
understanding of closed-loop control relationships (e.g. interpretation of frequency responses).
The function descriptions include examples that show how the closed-loop control is influenced
by the particular function. Further the descriptions of the functions provide information about
the measuring functions that are available for measuring the control loops (also see Chapter
"Configuring measuring functions (Page 584)").
The APC function module must be set before optimizing the position control.
Note
Increased CPU time for each drive axis as a result of APC
APC results in a significant increase in the CPU time required for each drive axis. As a
consequence, it cannot be guaranteed that 6 servo axes can be operated on one Control Unit
in all drive configurations. The number of axes must be reduced step-by-step if the CPU time
for the intended process is inappropriately high.
Applications
● Improve the higher-level position control
APC is deployed in order to improve the response of a position control (higher-level position
control with respect to the speed control). Damping critical oscillation in the speed control
loop often allows a higher position controller gain to be set. This is true, in particular, when
the position control uses a direct measuring system for the closed-loop control.
● Avoid oscillation and instability in the process
APC dampens oscillation resulting from periodic machining forces in the process (e.g high
load levels when machining steel), which cause oscillation to be excited or instability
(regenerative chatter). The process remains stable by dampening this oscillation. Higher
machining feed rates or increased swarf thickness are therefore possible.
● Avoid oscillation of the mechanical structure
Oscillations of the mechanical structure are excited in the process by the setpoint motion of
the axes. These oscillations have negative effects in the process (e.g. when finishing
surfaces in mold making), and the process has to be slowed down. Using APC, mechanical
structure oscillations can be dampened and the process made faster.
552
Function Manual, 06/2019, 6SL3097-5AB00-0BP2
Drive functions