February 2012 1 – 645
k
v
factor for
feedback control
with following error
The control loop gain - the k
v
factor - defines the amplification of the position control loop.
The k
v
factor is defined by the machine tool builder.
For axes that are interpolated with each other, the k
v
factors must be equal to prevent contour
deviations.
Interrelation of
k
v
factor, feed rate,
and following error
The following formula shows the interrelation of k
v
factor, feed rate, and following error:
or
Position control
with velocity
feedforward
The nominal velocity value consists of an open-loop and a closed-loop component.
With velocity feedforward control, the machine-adjusted nominal velocity value is the open-loop
controlled component. The closed-loop velocity component is calculated through the following error.
The following error is small (for example, several µm).
From the value in MP1392 (for the operating modes Positioning with manual data input, Programs
run / single block and Program run full sequence) and MP1391 (for the operating modes Manual
operation and El. handwheel) you can see, whether the machine is operated with following error or
velocity feedforward (for velocity feedforward control the bits are set to 1).
Figure: Simplified representation of velocity feedforward control
Control-loop parameters may only be changed by the machine manufacturer or after consultation
with the machine manufacturer!
An increase of the k
v
factor could lead to damage or injury to the machine or to persons!
k
v
= Loop gain (m/min)/mm]
v
e
= Rapid traverse [m/min]
s
a
= Following error [mm]
v
S
a
+
–
S
a
+
+
v
Δ t
MP1510.x
MP1080.x
v
Noml
Δ S
Noml
S
Noml
S
Actl
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