G2: Velocities, setpoint / actual value systems, closed-loop control
7.6 Optimization of the control
Basic Functions
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
381
Setting the equivalent time constant of the speed control loop
MD32810 speed feedforward control
We recommend that the axis be allowed to move in and out in "AUTOMATIC" mode with a parts program and
that travel-in to the target position, i.e., the actual position value of the active measuring system, be monitored
with servo trace.
The actual position value can also be output to the drive module's digital-to-analog converter, and an
oscilloscope can be used for monitoring.
The initial value for setting is the time constant of the speed control loop. This can be read from the reference
frequency characteristic of the speed control loop. In the frequent case of a PI controller with speed setpoint
smoothing, an approximate equivalent time can be read from drive machine data p1414, p1415, p1416 and
p1421.
Another option would be to trace the speed setpoint and actual value at a constant acceleration using an
oscilloscope and to measure the follow-on time of the speed actual value.
This start value (e.g. 1.5ms) is now entered:
MD32810 $MA_EQUIV_SPEEDCTRL_TIME = 0.0015
The axis then travels to and fro and the operator monitors a greatly-magnified characteristic of the position actual
value at the target position.
The following rules apply to making manual fine adjustments:
Magnifying MD32810
Increasing the value of MD32810 slows the axis down and increases the geometric contour error on curves to
some degree.
It has a similar effect to reducing the position controller gain:
MD32200 $MA_POSCTRL_GAIN
This can also be watched in the Diagnostics area in the screen form "Service Axis" based on the servo gain value
calculated.
Reducing MD32810
Reducing the value of MD32810 quickens the axis.
Therefore, MD32810 should be assigned as small a value as possible, with the overshoot setting the limit during
positioning.
Overshoot monitored: → magnify MD32810.
Excessively slow approach monitored: → reduce MD32810.
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