B. Basic controlling principles
B−38
Festo P.BE−CPX−CMA X−CONTROL−EN en 0908NH
B.8.2 Influence of the mass on standstill control
After completion of a positioning task, on−the−fly switch−over
from positioning control to force control occurs so as to en
sure safe standstill of the drive. The standstill force F
still
, to
which controlling is done, corresponds to the force on the
piston after the drive has reached its target position. It is
tapped by the cylinder 200 ms after MC, the following
applies:
F
still
= p
1−200ms
* A
1
p
2−200ms
* A
2
(p
1
and p
2
are the pressure values in the cylinder, 200 ms
after MC)
If towards the end of the positioning process the actual force
drifts so fast that it threatens to exceed friction hysteresis,
then the system switches directly to standstill control without
taking into account the delay time of 200 ms.
So in contrast
to force control, standstill control is not based
on calculated values that are dependent on configured mass
values, but on force values measured at the end of the posi
tioning process. Mass changes that are not specified in the
positioning records, do therefore not affect the behaviour of
the drive in the standstill
position.
Warning: When positioning, the drive comes to a standstill
within the static friction, so the standstill force can also vary
in the area of static friction. So the force the FCT displays dur
ing standstill varies from stroke to stroke.
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