Computer Drive Installation Instructions

12 Functional Descriptions 10.94
12.18.13 Start-up
Optimization of the compensatory controller
When it is activated, the compensatory controller basically increases the servo gain factor of
the following drive. However, if the axis or spindle-specific servo gain factor of the following
drive is already set to the maximum value, the following drive starts to oscillate if the
compensatory controller is activated. In this case, the resulting servo gain factor (sum of the
servo gain factors of the axes and compensatory controller) is too high. We therefore
recommend you to follow the procedure described below:
• Drive start-up for LINK OFF
The leading and following drives are separately parameterized (with the link deactivated)
according to the conventional method. The highest possible servo factors (LD-KV
max
and
FD-KV
max
) above which the position control loop tends to oscillate and become unstable
must be calculated.
• Drive start-up for LINK ON (P component)
– The P component of the compensatory controller (NC MD 1420*/487*) operating in
parallel acts as an additional servo gain factor for the following drive (FD-KV
CC
). The
gain factor FD-KV
Drv
of the following drive controller must therefore be set to a value
that is lower than the FD-KV
max
calculated beforehand. The servo gain factor of the
following drive (FD-KV
Drv
) must fulfil the following conditions:
FD-KV
max
FD-KV
Drv
(NC MD252*/435*..442*) [0.01/s]+ FD-KV
CC
(NC MD1420*/487*)
[1/s]
FD-KV
max
[FD-KV
Drv
(NC MD252*/435*..442*)+ 100* FD-KV
CC
(NC MD1420*/487*)]
[1/s]
– Actual value link with and without feedforward control
When an actual value link with or without feedforward control is used, we recommend
that FD-KV
CC
always be set to 0 (NC MD 1420*/487* = 0).
– Setpoint link without feedforward control
When a setpoint link without feedforward control is used, it is essential to set the
leading and following drive position control loops such that they both have the same
dynamic response to setpoint changes. If the P component of the compensatory
controller is applied, the following drive must have a better dynamic response, and
therefore a higher maximum servo gain factor (FD-KV
max
), than the leading drive.
Effectively, however, the same servo gain factor is set for the following drive as for the
leading drive.
The value of LD-KV
max
is calculated first and entered in NC MD 252*/435*..442* of the
leading drive. The same dynamic response to setpoint changes is now set for the
following drive by means of FD-KV
Drv
(NC MD 252*/435*..442*). The value calculated for
LD-KV
max
is entered for this purpose. The differential value up to FD-KV
max
is applied
for FD-KV
CC
.
– Setpoint link with feedforward control
When a setpoint link with feedforward control is used, it is not necessary to set the
leading and following drives such that they both have the same dynamic response to
setpoint changes. It is also not necessary for the following axis to be more dynamic by
setting FD-KV
max
> LD-KV
max
when the P-component of the compensatory controller
is applied. There is also no need to set the servo gain factors in the leading and
following drive position control loops to the same value.
The dynamic response of the drives is matched by means of setpoint smoothing filters
and feedforward control action. The best possible response of the GI grouping to distur-
bances and setpoint changes can be obtained by means of 100 % feedforward control
with appropriately set setpoint smoothing and balancing filters (no positional overshoot
during rapid traversal). Please refer to the functional description of "Feedforward
control" for further information about setting setpoint smoothing filters and the
feedforward control function.
_______
1) Please note "Parameter set switchover" function description with SW 4 and higher.
12–162 © Siemens AG 1992 All Rights Reserved 6FC5197- AA50
SINUMERIK 840C (IA)