Siemens SINUMERIK 840Di Function Manual page 438

Detailed Description
2.5 Optimization of the control
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
part 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 (HMI Advanced or programming
device). 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 proportional-plus-integral-action controller with special value smoothing, an approximate
equivalent time can be read from drive machine data 1500-1503.
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 initial value (e.g. 1.5 ms) is then 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:
Overshoot monitored:
Excessively slow approach monitored:
Magnifying MD32810
Magnifying the value in machine data:
MD32810 $MA_EQUIV_SPEEDCTRL_TIME
slows the axis down and increases the geometric contour error on curves.
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 in machine data:
MD32810 $MA_EQUIV_SPEEDCTRL_TIME
speeds the axis up.
Therefore, MD32810 should be assigned as small a value as possible, with the overshoot
setting the limit during positioning.
2-64
Magnify MD32810 $MA_EQUIV_SPEEDCTRL_TIME.
Reduce MD32810 $MA_EQUIV_SPEEDCTRL_TIME.
Velocities, Setpoint/Actual-Value Systems, Closed-Loop Control (G2)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0